Stops xenos from bypassing dead moving via roller beds (#3810)

# About the pull request

This PR makes it so a roller bed with a dead person on it now is
unmovable. Can still be moved if unconscious or alive so as to mimic
current restrictions.

# Explain why it's good for the game

This has been a longstanding ruling issue that we can now just let be
mechanically prevented. Less rule bloat good.


# Testing Photographs and Procedure
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<summary>Screenshots & Videos</summary>

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screenshots and the `<details>` tags.

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# Changelog

:cl: Morrow
fix: Stops xenos from bypassing dead moving via roller beds
/:cl:

code/game/objects/structures/stool_bed_chair_nest/bed.dm

@@ -208,6 +208,20 @@
 			return
 	..()
 
+/obj/structure/bed/roller/Collided(atom/movable/moving_atom)
+	if(!isxeno(moving_atom))
+		return ..()
+
+	if(buckled_mob && buckled_mob.stat != DEAD)
+		return ..()
+
+	if(buckled_bodybag)
+		var/mob/mob_in_bodybag = locate(/mob) in buckled_bodybag
+		if(mob_in_bodybag && mob_in_bodybag.stat != DEAD)
+			return ..()
+
+	return
+
 /obj/item/roller
 	name = "roller bed"
 	desc = "A collapsed roller bed that can be carried around."