Merge pull request #6810 from janjust/v4.0.x

v4.0.x OSC: Reset external request to NULL

ompi/mca/osc/ucx/osc_ucx_request.c

@@ -55,6 +55,7 @@ void req_completion(void *request, ucs_status_t status) {
 
     if(req->external_req != NULL) {
         ompi_request_complete(&(req->external_req->super), true);
+        req->external_req = NULL;
         ucp_request_release(req);
         mca_osc_ucx_component.num_incomplete_req_ops--;
         assert(mca_osc_ucx_component.num_incomplete_req_ops >= 0);