MPRIS: can_go_previous should always be true

[eulerfan271]

Describe your changes

Currently, the MPRIS previous does nothing when the song is the first in the queue, when it should restart the song (as is the case if one uses the previous keyboard shortcut in the TUI). This can fixed by making the MPRIS function can_go_previous identically true, rather than checking if there's a previous song in the queue.

Issue ticket number and link

One might consider this is somewhat related to #1110?

Checklist before requesting a review

• Documentation was updated (i.e. due to changes in keybindings, commands, etc.)
• Changelog was updated with relevant user-facing changes (eg. not dependency updates,
  not performance improvements, etc.)

[hrkfdn]

Hey! Thanks for the PR. Should we at least check whether a track is loaded or similar, to disable the previous command if the queue is completely empty, for instance?

Also curious how other plays handle this. The specs aren't very specific about it..

[eulerfan271]

Good point, thanks for the quick review! I've updated it to be true only if something is in the queue; it now matches many of the other MPRIS functions (play, pause, etc).

As for other players, I think this behavior (calling "previous" on the first song in the queue repeats that song) is pretty common, and it's present in both ncspot (when using the commands in the TUI) and the official Spotify app. In my opinion, it's also more useful/intuitive than the previous key doing nothing.

[hrkfdn]

LGTM, let's get it in!