Fixed walls not splitting zones.

code/ZAS/Zone.dm

@@ -107,6 +107,7 @@ Class Procs:
 	#endif
 
 /zone/proc/rebuild()
+	if(invalid) return //Short circuit for explosions where rebuild is called many times over.
 	c_invalidate()
 	for(var/turf/simulated/T in contents)
 		//T.dbg(invalid_zone)

code/ZAS/_docs.dm

@@ -27,7 +27,7 @@ Notes for people who used ZAS before:
 
 */
 
-//#define ZASDBG
+#define ZASDBG
 //#define ZLEVELS
 
 #define AIR_BLOCKED 1