Add PlayerProxy missing current track when created after loading

[acolombier]

This PR fixes the issue where a QMLPlayerProxy is missing the currently loaded track. Currently, if you create a QMLPlayerProxy (or PlayerProxy in QML) while a track is already loaded on a player, the PlayerProxy will appears as if no track was loaded.

This can can be reproduced by

• Opening the QML interface
• Load a track on a deck
• Triggering a reload (e.g touch res/qml/main.qml)

Without this fix, the deck will appears as if empty. With it, and will display correctly, with the loaded track.

[daschuer]

LGTM, Thank you.