Extract guard gold before disposing it

If the gold is still in monster inventory, dealloc_obj will panic.

src/steal.c

@@ -676,6 +676,7 @@ boolean is_pet; /* If true, pet should keep wielded/worn items */
         if (canspotmon(mtmp))
             pline("%s gold %s.", s_suffix(Monnam(mtmp)),
                   canseemon(mtmp) ? "vanishes" : "seems to vanish");
+        obj_extract_self(otmp);
         obfree(otmp, (struct obj *) 0);
     } /* isgd && has gold */