Stops welding wood containers. (#3816)

# About the pull request
It doesn't make sense you can weld wood coffins and the like closed.
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# Explain why it's good for the game
LOGIC
# Testing Photographs and Procedure
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<summary>Screenshots & Videos</summary>

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</details>


# Changelog
:cl:
fix: You can no longer weld non metal containers closed.
/:cl:

code/game/objects/structures/crates_lockers/closets.dm

@@ -245,19 +245,22 @@
 	else if(istype(W, /obj/item/packageWrap) || istype(W, /obj/item/explosive/plastic))
 		return
 	else if(iswelder(W))
+		if(material != MATERIAL_METAL && material != MATERIAL_PLASTEEL)
+			to_chat(user, SPAN_WARNING("You cannot weld [material]!"))
+			return FALSE//Can't weld wood/plastic.
 		if(!HAS_TRAIT(W, TRAIT_TOOL_BLOWTORCH))
 			to_chat(user, SPAN_WARNING("You need a stronger blowtorch!"))
-			return
+			return FALSE
 		var/obj/item/tool/weldingtool/WT = W
 		if(!WT.isOn())
 			to_chat(user, SPAN_WARNING("\The [WT] needs to be on!"))
-			return
+			return FALSE
 		if(!WT.remove_fuel(0, user))
 			to_chat(user, SPAN_NOTICE("You need more welding fuel to complete this task."))
-			return
+			return FALSE
 		playsound(src, 'sound/items/Welder.ogg', 25, 1)
 		if(!do_after(user, 10 * user.get_skill_duration_multiplier(SKILL_CONSTRUCTION), INTERRUPT_ALL|BEHAVIOR_IMMOBILE, BUSY_ICON_BUILD))
-			return
+			return FALSE
 		welded = !welded
 		update_icon()
 		for(var/mob/M as anything in viewers(src))
@@ -266,9 +269,9 @@
 		if(isxeno(user))
 			var/mob/living/carbon/xenomorph/opener = user
 			src.attack_alien(opener)
-			return
+			return FALSE
 		src.attack_hand(user)
-	return
+	return TRUE
 
 /obj/structure/closet/MouseDrop_T(atom/movable/O, mob/user)
 	if(!opened)