windows crash: during shutdown the IOCP wake signal handle is cleaned up but there might still be a pending event that gets delivered. Make sure we don't try to access the pointer in this situation.

src/lib/ares_event_win32.c

@@ -793,7 +793,11 @@ static void ares_evsys_win32_event_mod(ares_event_t      *event,
 static ares_bool_t ares_evsys_win32_process_other_event(
   ares_evsys_win32_t *ew, ares_evsys_win32_eventdata_t *ed, size_t i)
 {
-  ares_event_t *event = ed->event;
+  ares_event_t *event;
+
+  /* NOTE: do NOT dereference 'ed' if during shutdown as this could be an
+   * invalid pointer if the signal handle was cleaned up, but there was still a
+   * pending event! */
 
   if (ew->is_shutdown) {
     CARES_DEBUG_LOG("\t\t** i=%lu, skip non-socket handle during shutdown\n",
@@ -801,6 +805,7 @@ static ares_bool_t ares_evsys_win32_process_other_event(
     return ARES_FALSE;
   }
 
+  event = ed->event;
   CARES_DEBUG_LOG("\t\t** i=%lu, ed=%p (data)\n", (unsigned long)i, (void *)ed);
 
   event->cb(event->e, event->fd, event->data, ARES_EVENT_FLAG_OTHER);