Router: fixing crash after WebSocket processing.

After WebSocket processing, the application port was released with incorrect
reason ("got request"), unnecessarily decrementing the active request counter.

The assertion was triggered only on application removal; a test was added
for this case.

src/nxt_router.c

@@ -3796,7 +3796,10 @@ nxt_router_response_ready_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg,
         nxt_buf_chain_add(&b, nxt_http_buf_last(r));
 
         req_rpc_data->rpc_cancel = 0;
-        req_rpc_data->apr_action = NXT_APR_GOT_RESPONSE;
+
+        if (req_rpc_data->apr_action == NXT_APR_REQUEST_FAILED) {
+            req_rpc_data->apr_action = NXT_APR_GOT_RESPONSE;
+        }
 
         nxt_request_rpc_data_unlink(task, req_rpc_data);