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
public:
  FileChooserDialog(GtkFileChooserAction action,
                    atom::NativeWindow* parent_window,
                    const std::string& title,
                    const std::string& button_label,
                    const base::FilePath& default_path,
                    const Filters& filters)
      : parent_(static_cast<atom::NativeWindowViews*>(parent_window)),
        dialog_scope_(parent_window),
        filters_(filters) {
    const char* confirm_text = GTK_STOCK_OK;
    if (!button_label.empty())
      confirm_text = button_label.c_str();
    else if (action == GTK_FILE_CHOOSER_ACTION_SAVE)
      confirm_text = GTK_STOCK_SAVE;
    else if (action == GTK_FILE_CHOOSER_ACTION_OPEN)
      confirm_text = GTK_STOCK_OPEN;
    dialog_ = gtk_file_chooser_dialog_new(
        title.c_str(),