Merge pull request #29263 from trociny/wip-rbd-external_callback

librbd: don't use complete_external_callback if ImageCtx destroyed

Reviewed-by: Jason Dillaman <dillaman@redhat.com>

src/librbd/io/AioCompletion.cc

@@ -95,6 +95,7 @@ void AioCompletion::complete() {
     // must destroy ImageCtx prior to invoking callback
     delete ictx;
     ictx = nullptr;
+    external_callback = false;
   }
 
   state = AIO_STATE_CALLBACK;