Fix digging through iron bars from adjacent pit

It was possible to create a pit on top of iron bars, by first creating
a pit next to the bars, going down into the pit, and then digging sideways
towards the bars. This did not destroy the iron bars.

doc/fixes37.0

@@ -52,6 +52,7 @@ poly'd hero was able to zap wands, apply tools, and #rub objects without
 	having any hands
 spellcasting monster got an extra move after casting
 allow defining #wizgenesis quantity in the prompt
+digging through iron bars from an adjacent pit made a pit on top of the bars
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository

src/dig.c

@@ -1635,6 +1635,7 @@ char *msg;
     } else if (ltyp == IRONBARS) {
         /* "set of iron bars" */
         Strcpy(msg, "The bars go much deeper than your pit.");
+        return FALSE;
 #if 0
     } else if (is_lava(cc->x, cc->y)) {
     } else if (is_ice(cc->x, cc->y)) {