mpi/src/starpu_mpi.c: fix #19980, the code was not dead

mpi/src/starpu_mpi.c

@@ -1370,7 +1370,7 @@ static void *_starpu_mpi_progress_thread_func(void *arg)
 		starpu_pthread_wait_reset(&wait);
 #endif
 		/* shall we block ? */
-		unsigned block = _starpu_mpi_req_list_empty(ready_requests) && _starpu_mpi_early_request_count() == 0 && _starpu_mpi_sync_data_count() == 0;
+		unsigned block = _starpu_mpi_req_list_empty(ready_requests) && _starpu_mpi_early_request_count() == 0 && _starpu_mpi_sync_data_count() == 0 && _starpu_mpi_req_list_empty(detached_requests);
 
 		if (block)
 		{