I'm encountering a very weird issue, only in GNU/Linux.

Consider the following gist that shows an open dialog and presents the resulting filename in the screen: https://gist.github.com/jviotti/b8358165f1694228fbc31e400dbadab6, which you can run by `npm install && npm start`.

Now create a file with a `.img.gz` extension, like `foo.img.gz`. Using the `touch` command is enough.

Try to select it using the gist application. The `.img.gz` extension is replaced by `.zip` (or whatever is the first item of the extensions filter) for some strange reason.

The issue only seems reproducible with files containing multiple extensions, and when a dialog filter is present.
- Electron version: 1.2.5
- Operating system: GNU/Linux (Ubuntu 14.04 and Arch Linux)

atom/browser/ui/file_dialog_gtk.cc
const gchar* filename) const {
  base::FilePath path(filename);
  GtkFileFilter* selected_filter =
      gtk_file_chooser_get_filter(GTK_FILE_CHOOSER(dialog_));
  if (!selected_filter)
    return path;
  GSList* filters = gtk_file_chooser_list_filters(GTK_FILE_CHOOSER(dialog_));
  int i = g_slist_index(filters, selected_filter);
  g_slist_free(filters);
  if (i >= filters_.size())
    return path;
  const auto& extensions = filters_[i].second;
  for (const auto& extension : extensions) {
    if (extension == "*" || path.MatchesExtension("." + extension))
      return path;
  }
  return path.ReplaceExtension(extensions[0]);
}
}  
bool ShowOpenDialog(atom::NativeWindow* parent_window,