Adding null pointer check (followup to r13240).

git-svn-id: https://svn.code.sf.net/p/rathena/svn/trunk@13243 54d463be-8e91-2dee-dedb-b68131a5f0ec

src/map/clif.c

@@ -2399,7 +2399,7 @@ void clif_changelook(struct block_list *bl,int type,int val)
 	}
 
 	// prevent leaking the presence of GM-hidden objects
-	if( sc->option&OPTION_INVISIBLE )
+	if( sc && sc->option&OPTION_INVISIBLE )
 		target = SELF;
 
 #if PACKETVER < 4