Fix album shuffle issue

Hi,

This pull request addresses issue #4402 where after restarting Clementine in shuffle album mode, the current album was skipped after playing one track.

The change tests if a track is selected (despite being paused or stopped) and the user simply hits play, it will prioritize that music's album and won't skip the album after playing one track. The difference is that it doesn't only check if the track is **currently** playing, but as in account if it also selected.

Thanks!
Waiting feedback.
Yes, the issue happens in other situations also. Just have a different shuffle mode and music stopped (no pause), change to shuffle album and then just hit play. It will jump to another album after the first song (which is the previously selected song). I made a comment in the issue regarding what I think it means to be selected according to my tests. What happens is that the shuffle only prioritizes the album of a song that is currently playing, so any situation where no track was playing and you changed the shuffle mode, the bug would manifest. What I did was to make it consider selected tracks and therefore making the comment a bit more general by mentioning the "being selected" rather than saying "when we restart clementine".

Thanks