VLCNetworkServerBrowserViewController: Properly stop the activity indicator + remove the play all button when necessary
This merge request brings a fix to:
- The activity indicator that is now properly stopped when the folder selected has already been parsed and is empty.
This merge request also brings an addition to the navigation bar buttons with:
- The play all button that is now hidden when necessary to avoid having it being displayed when the view is empty.
This relies on several changes brought by: