Fix remaining non-returning Destroys()

Plus a little refactor to mining flaps and spacepod doors- they now use
CanAtmosPass instead of manually setting the turf to no-atmos-passing

code/game/gamemodes/blob/blobs/core.dm

@@ -25,8 +25,7 @@
 		if(overmind)
 			del(overmind)
 		processing_objects.Remove(src)
-		..()
-		return
+		return ..()
 
 	update_icon()
 		if(health <= 0)