ompi/request: Check for REQUEST_COMPLETED in threaded check

 * It is possible for us to get to this selection statement with `tmp_sync`
   set to `REQUEST_COMPLETED` which causes a segv when we try to dereference
   that value inside `wait_sync_update`. So check against both `REQUEST_PENDING`
   and `REQUEST_COMPLETED` before attempting that function.

Author: jjhursey

ompi/request/request.h

@@ -428,7 +428,7 @@ static inline int ompi_request_complete(ompi_request_t* request, bool with_signa
                 ompi_wait_sync_t *tmp_sync = (ompi_wait_sync_t *) OPAL_ATOMIC_SWAP_PTR(&request->req_complete,
                                                                                        REQUEST_COMPLETED);
                 /* In the case where another thread concurrently changed the request to REQUEST_PENDING */
-                if( REQUEST_PENDING != tmp_sync )
+                if( REQUEST_PENDING != tmp_sync && REQUEST_COMPLETED != tmp_sync )
                     wait_sync_update(tmp_sync, 1, request->req_status.MPI_ERROR);
             }
         } else