alternate fix issue #938 - use-after-free

If you kill an engulfer and get dropped onto a level teleporter or
magic portal, wait until end of turn to perform the level change.
The code to finish off killing the engulfer was left with a stale
pointer for the monster when level change happens immediately.

The level change was being forced to be immediate so that something
noticable happened before being asked for what to name a teleport
scroll read while cursed or confused, but such scrolls become
discovered these days.  So when no prompting for what to call the
scroll takes place, there's no need to change levels instantly.

This issue was just fixed but this commit is simpler.  The previous
fix is left in place in case some other level change path is--or
becomes--possible.

src/teleport.c

@@ -1110,11 +1110,18 @@ level_tele(void)
                   Verbose(2, level_tele)
                       ? "You materialize on a different level!"
                       : (char *) 0);
+#if 0   /* always wait until end of turn to change level, otherwise code
+         * that references monsters as this call stack unwinds won't be
+         * able to access them reliably; the do-the-change-now code here
+         * dates from when reading a scroll of teleportation wouldn't
+         * always make the scroll become discovered but that's no longer
+         * the case so it shouldn't be needed anymore */
 
     /* in case player just read a scroll and is about to be asked to
        call it something, we can't defer until the end of the turn */
     if (u.utotype && !gc.context.mon_moving)
         deferred_goto();
+#endif
 }
 
 void