data_request: Fix memory leak on prefetch getting ENOMEM

src/datawizard/data_request.c

@@ -556,6 +556,11 @@ static int starpu_handle_data_request(struct _starpu_data_request *r, unsigned m
 	{
 		/* If there was not enough memory, we will try to redo the
 		 * request later. */
+
+		if (r->prefetch > STARPU_FETCH)
+			/* Drop ref until next try */
+			dst_replicate->refcnt--;
+
 		_starpu_spin_unlock(&handle->header_lock);
 		return -ENOMEM;
 	}