Fix explosions damaging rod form wizards and supply pod contents (#40758)

The issue was that when casting rod form, the wizard is forceMoved() into the
rod. When an epicenter explosion happens, explosion.dm forcibly goes through
the contents of EVERYTHING, and calls ex_act().

This caused the wizard in the contents of the rod to get damaged by epicenter
explosions (ie if they hit a fuel tank in rod form)

code/datums/explosion.dm

@@ -198,7 +198,7 @@ GLOBAL_LIST_EMPTY(explosions)
 			var/list/items = list()
 			for(var/I in T)
 				var/atom/A = I
-				if (A.contents_explosion()) //The atom/contents_explosion() proc returns null if the contents ex_acting has been handled by the atom, and TRUE if it hasn't.
+				if (!A.prevent_content_explosion()) //The atom/contents_explosion() proc returns null if the contents ex_acting has been handled by the atom, and TRUE if it hasn't.
 					items += A.GetAllContents()
 			for(var/O in items)
 				var/atom/A = O

code/game/atoms.dm

@@ -294,8 +294,11 @@
 		to_chat(user, "<span class='warning'>You can't move while buckled to [src]!</span>")
 	return
 
+/atom/proc/prevent_content_explosion()
+	return FALSE
+
 /atom/proc/contents_explosion(severity, target)
-	return TRUE //Return TRUE if the contents_explosion has not been overridden.
+	return //For handling the effects of explosions on contents that would not normally be effected
 
 /atom/proc/ex_act(severity, target)
 	set waitfor = FALSE

code/modules/cargo/supplypod.dm

@@ -87,6 +87,9 @@
 /obj/structure/closet/supplypod/contents_explosion() //Supplypods also protect their contents from the harmful effects of fucking exploding.
 	return
 
+/obj/structure/closet/supplypod/prevent_content_explosion() //Useful for preventing epicenter explosions from damaging contents
+	return TRUE
+
 /obj/structure/closet/supplypod/toggle(mob/living/user) //Supplypods shouldn't be able to be manually opened under any circumstances, as the open() proc generates supply order datums
 	return
 

code/modules/events/immovable_rod.dm

@@ -100,6 +100,9 @@ In my current plan for it, 'solid' will be defined as anything with density == 1
 	walk(src,0)
 	walk_towards(src, destination, 1)
 
+/obj/structure/closet/supplypod/prevent_content_explosion()
+	return TRUE
+
 /obj/effect/immovablerod/ex_act(severity, target)
 	return 0