quiet a number of macosx warnings

src/mkmaze.c

@@ -1602,7 +1602,7 @@ restore_waterlevel(nhfp)
 NHFILE *nhfp;
 {
     struct bubble *b = (struct bubble *) 0, *btmp;
-    int i, n;
+    int i, n = 0;
 
     if (!Is_waterlevel(&u.uz) && !Is_airlevel(&u.uz))
         return;