message: Fix gst_initializer
  Use the return value of gst_init_check instead of testing the error pointer
diff: @@ -216,10 +216,10 @@ private:
  call_deinit = utils::getConfigurationParameterBool("OPENCV_VIDEOIO_GSTREAMER_CALL_DEINIT", false);
  GSafePtr<GError> err;
  - gst_init_check(NULL, NULL, err.getRef());
  - if (err)
  + gboolean gst_init_res = gst_init_check(NULL, NULL, err.getRef());
  + if (!gst_init_res)
  {
  - CV_WARN("Can't initialize GStreamer: " << err->message);
  + CV_WARN("Can't initialize GStreamer: " << (err ? err->message : "<unknown reason>"));
  isFailed = true;
  return;
  }
  