qrexec: better handle remote process termination

If remote end terminates without proper protocol finish
(MSG_DATA_EXIT_CODE), terminate also local part instead of waiting
indefinitely.

qrexec/qrexec-agent-data.c

@@ -296,12 +296,21 @@ int process_child_io(libvchan_t *data_vchan,
 
         /* if all done, exit the loop */
         if ((!child_process_pid || child_process_status > -1) &&
+                (child_process_pid || remote_process_status > -1) &&
                 stdin_fd == -1 && stdout_fd == -1 && stderr_fd == -1) {
             if (child_process_status > -1) {
                 send_exit_code(data_vchan, child_process_status);
             }
             break;
         }
+        /* also if vchan is disconnected (and we processed all the data), there
+         * is no sense of processing further data */
+        if (!libvchan_data_ready(data_vchan) && !libvchan_is_open(data_vchan)) {
+            if (child_process_pid)
+                return remote_process_status;
+            else
+                return child_process_status;
+        }
         /* child signaled desire to use single socket for both stdin and stdout */
         if (stdio_socket_requested) {
             if (stdout_fd != -1)