Lurker: bug fix, var disambiguation and redundant type checks (#4922)

- Fixes #4905
- Disambiguates some abbreviated vars & single letter
- Removes some unnecessary type checks

# Explain why it's good for the game
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
fix: Lurker can no longer tail jab through doors/structures.
code: Var disambiguation, cleanup and removal of redundant typechecks in
lurker code.
/:cl:

code/modules/mob/living/carbon/xenomorph/abilities/lurker/lurker_abilities.dm

@@ -30,20 +30,20 @@
 			if (istype(lurker_invis))
 				lurker_invis.invisibility_off()
 
-/datum/action/xeno_action/activable/pounce/lurker/additional_effects(mob/living/L)
-	var/mob/living/carbon/xenomorph/X = owner
-	if (!istype(X))
+/datum/action/xeno_action/activable/pounce/lurker/additional_effects(mob/living/living_mob)
+	var/mob/living/carbon/xenomorph/xeno = owner
+	if (!istype(xeno))
 		return
 
-	if (X.mutation_type == LURKER_NORMAL)
-		RegisterSignal(X, COMSIG_XENO_SLASH_ADDITIONAL_EFFECTS_SELF, PROC_REF(remove_freeze), TRUE) // Suppresses runtime ever we pounce again before slashing
+	if (xeno.mutation_type == LURKER_NORMAL)
+		RegisterSignal(xeno, COMSIG_XENO_SLASH_ADDITIONAL_EFFECTS_SELF, PROC_REF(remove_freeze), TRUE) // Suppresses runtime ever we pounce again before slashing
 
-/datum/action/xeno_action/activable/pounce/lurker/proc/remove_freeze(mob/living/carbon/xenomorph/X)
+/datum/action/xeno_action/activable/pounce/lurker/proc/remove_freeze(mob/living/carbon/xenomorph/xeno)
 	SIGNAL_HANDLER
 
-	var/datum/behavior_delegate/lurker_base/BD = X.behavior_delegate
-	if (istype(BD))
-		UnregisterSignal(X, COMSIG_XENO_SLASH_ADDITIONAL_EFFECTS_SELF)
+	var/datum/behavior_delegate/lurker_base/behaviour_del = xeno.behavior_delegate
+	if (istype(behaviour_del))
+		UnregisterSignal(xeno, COMSIG_XENO_SLASH_ADDITIONAL_EFFECTS_SELF)
 		end_pounce_freeze()
 
 /datum/action/xeno_action/onclick/lurker_invisibility

code/modules/mob/living/carbon/xenomorph/abilities/lurker/lurker_powers.dm

@@ -208,6 +208,9 @@
 				xeno.visible_message(SPAN_XENOWARNING("\The [xeno] strikes the window with their tail!"), SPAN_XENOWARNING("You strike the window with your tail!"))
 				apply_cooldown(cooldown_modifier = 0.5)
 				return
+			if(current_structure.density)
+				to_chat(xeno, SPAN_WARNING("There's something blocking you from striking!"))
+				return
 
 	if(!isxeno_human(hit_target) || xeno.can_not_harm(hit_target) || hit_target.stat == DEAD)
 		xeno.visible_message(SPAN_XENOWARNING("\The [xeno] swipes their tail through the air!"), SPAN_XENOWARNING("You swipe your tail through the air!"))

code/modules/mob/living/carbon/xenomorph/castes/Lurker.dm

@@ -84,7 +84,7 @@
 		target_carbon.set_effect(get_xeno_stun_duration(target_carbon, 3), SUPERSLOW)
 		next_slash_buffed = FALSE
 		var/datum/action/xeno_action/onclick/lurker_assassinate/ability = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/onclick/lurker_assassinate)
-		if (ability && istype(ability))
+		if (ability)
 			ability.button.icon_state = "template"
 
 	return original_damage
@@ -110,33 +110,33 @@
 /datum/behavior_delegate/lurker_base/melee_attack_additional_effects_self()
 	..()
 
-	var/datum/action/xeno_action/onclick/lurker_invisibility/LIA = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/onclick/lurker_invisibility)
-	if (LIA && istype(LIA))
-		LIA.invisibility_off()
+	var/datum/action/xeno_action/onclick/lurker_invisibility/lurker_invis_action = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/onclick/lurker_invisibility)
+	if (lurker_invis_action)
+		lurker_invis_action.invisibility_off()
 
 /datum/behavior_delegate/lurker_base/proc/decloak_handler(mob/source)
 	SIGNAL_HANDLER
-	var/datum/action/xeno_action/onclick/lurker_invisibility/LIA = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/onclick/lurker_invisibility)
-	if(istype(LIA))
-		LIA.invisibility_off()
+	var/datum/action/xeno_action/onclick/lurker_invisibility/lurker_invis_action = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/onclick/lurker_invisibility)
+	if(istype(lurker_invis_action))
+		lurker_invis_action.invisibility_off()
 
 // What to do when we go invisible
 /datum/behavior_delegate/lurker_base/proc/on_invisibility()
-	var/datum/action/xeno_action/activable/pounce/lurker/LPA = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/activable/pounce/lurker)
-	if (LPA && istype(LPA))
-		LPA.knockdown = TRUE // pounce knocks down
-		LPA.freeze_self = TRUE
+	var/datum/action/xeno_action/activable/pounce/lurker/lurker_pounce_action = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/activable/pounce/lurker)
+	if (lurker_pounce_action)
+		lurker_pounce_action.knockdown = TRUE // pounce knocks down
+		lurker_pounce_action.freeze_self = TRUE
 	ADD_TRAIT(bound_xeno, TRAIT_CLOAKED, TRAIT_SOURCE_ABILITY("cloak"))
 	RegisterSignal(bound_xeno, COMSIG_MOB_EFFECT_CLOAK_CANCEL, PROC_REF(decloak_handler))
 	bound_xeno.stealth = TRUE
 	can_go_invisible = FALSE
 	invis_start_time = world.time
 
 /datum/behavior_delegate/lurker_base/proc/on_invisibility_off()
-	var/datum/action/xeno_action/activable/pounce/lurker/LPA = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/activable/pounce/lurker)
-	if (LPA && istype(LPA))
-		LPA.knockdown = FALSE // pounce no longer knocks down
-		LPA.freeze_self = FALSE
+	var/datum/action/xeno_action/activable/pounce/lurker/lurker_pounce_action = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/activable/pounce/lurker)
+	if (lurker_pounce_action)
+		lurker_pounce_action.knockdown = FALSE // pounce no longer knocks down
+		lurker_pounce_action.freeze_self = FALSE
 	bound_xeno.stealth = FALSE
 	REMOVE_TRAIT(bound_xeno, TRAIT_CLOAKED, TRAIT_SOURCE_ABILITY("cloak"))
 	UnregisterSignal(bound_xeno, COMSIG_MOB_EFFECT_CLOAK_CANCEL)
@@ -153,9 +153,9 @@
 
 	can_go_invisible = TRUE
 	if(bound_xeno)
-		var/datum/action/xeno_action/onclick/lurker_invisibility/LIA = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/onclick/lurker_invisibility)
-		if(LIA && istype(LIA))
-			LIA.end_cooldown()
+		var/datum/action/xeno_action/onclick/lurker_invisibility/lurker_invisibility_action = get_xeno_action_by_type(bound_xeno, /datum/action/xeno_action/onclick/lurker_invisibility)
+		if(lurker_invisibility_action)
+			lurker_invisibility_action.end_cooldown()
 
 /datum/behavior_delegate/lurker_base/append_to_stat()
 	. = list()