Fixes drawing weapons when knocked down (#6569)

# About the pull request
Prevents you from drawing weapons when you are knocked down
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# Explain why it's good for the game
When you draw a weapon and are knocked down it will simply drop the
weapon since you can't hold it which is pretty annoying.
# Testing Photographs and Procedure
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<summary>Screenshots & Videos</summary>

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# Changelog
:cl:
fix: Fixes being able to draw weapons when knocked down
/:cl:

Co-authored-by: harryob <[email protected]>

code/modules/projectiles/gun_helpers.dm

@@ -530,7 +530,7 @@ DEFINES in setup.dm, referenced here.
 /mob/living/carbon/human/verb/holster_verb(unholster_number_offset = 1 as num)
 	set name = "holster"
 	set hidden = TRUE
-	if(usr.is_mob_incapacitated(TRUE) || usr.is_mob_restrained())
+	if(usr.is_mob_incapacitated(TRUE) || usr.is_mob_restrained() || IsKnockDown() || HAS_TRAIT_FROM(src, TRAIT_UNDENSE, LYING_DOWN_TRAIT))
 		to_chat(src, SPAN_WARNING("You can't draw a weapon in your current state."))
 		return