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
for (size_t i = 0; i < filters.size(); ++i) {
    const Filter& filter = filters[i];
    GtkFileFilter* gtk_filter = gtk_file_filter_new();
    for (size_t j = 0; j < filter.second.size(); ++j) {
      std::unique_ptr<std::string> file_extension(
          new std::string("." + filter.second[j]));
      gtk_file_filter_add_custom(
          gtk_filter,
          GTK_FILE_FILTER_FILENAME,
          reinterpret_cast<GtkFileFilterFunc>(FileFilterCaseInsensitive),
          file_extension.release(),
          reinterpret_cast<GDestroyNotify>(OnFileFilterDataDestroyed));
    }
    gtk_file_filter_set_name(gtk_filter, filter.first.c_str());
    gtk_file_chooser_add_filter(GTK_FILE_CHOOSER(dialog_), gtk_filter);
  }
}
base::FilePath FileChooserDialog::AddExtensionForFilename(