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
gtk_widget_destroy(dialog_);
    if (parent_)
      parent_->SetEnabled(true);
  }
  void RunAsynchronous() {
    g_signal_connect(dialog_, "delete-event",
                     G_CALLBACK(gtk_widget_hide_on_delete), NULL);
    g_signal_connect(dialog_, "response",
                     G_CALLBACK(OnFileDialogResponseThunk), this);
    gtk_widget_show_all(dialog_);
    
    
    int time = views::X11DesktopHandler::get()->wm_user_time_ms();
    gtk_window_present_with_time(GTK_WINDOW(dialog_), time);
  }
  void RunSaveAsynchronous(const SaveDialogCallback& callback) {