Fix hiding under nonexistent obj

Zapping a wand of teleportation at a location with object and
a monster hiding under it, but with the level full of monsters,
the monster would stay hidden even when the object was moved.

src/zap.c

@@ -2210,7 +2210,12 @@ bhito(struct obj *obj, struct obj *otmp)
             break;
         case WAN_TELEPORTATION:
         case SPE_TELEPORT_AWAY:
-            (void) rloco(obj);
+            {
+                coordxy ox = obj->ox, oy = obj->oy;
+
+                (void) rloco(obj);
+                maybe_unhide_at(ox, oy);
+            }
             break;
         case WAN_MAKE_INVISIBLE:
             break;