core: Reset stream title after all title tag changes.

[kingosticks]

Fixes #1871

PR #1751 introduced a regression where, following a normal gapless
track change, the stream_title was incorrectly set to the previous
track's title.

This still isn't very good as we are still emitting the bogus stream_title_changed event for the previous track's title. That is because we keep any tags we get after about_to_finish fires in pending_tags, and then emit them when the track change completes (on_stream_start fires), even if they were old tags for the previous track.

[codecov]

Codecov Report

Merging #1875 into develop will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           develop   #1875      +/-   ##
==========================================
+ Coverage    76.89%   76.9%   +<.01%     
==========================================
  Files           55      55              
  Lines         4666    4667       +1     
==========================================
+ Hits          3588    3589       +1     
  Misses        1078    1078

Impacted Files	Coverage Δ
mopidy/core/actor.py	94.59% <100%> (+0.03%)	⬆️

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[kingosticks]

I guess we could return if the current track has a file: uri but that would only restrict the issue to non-stream http tracks like gmusic etc. Still need a better way to work out what is a stream and what isn't.

[leaty]

I've been looking into this a little bit. @kingosticks Does mopidy know what is or isn't a stream at any point, or is that information lost after the backend extension?

[kingosticks]

It doesn't know. One proposition was to extend our Track model to include that.

…

On Thu, 30 Jan 2020, 08:14 leaty, ***@***.***> wrote: I've been looking into this a little bit. @kingosticks <https://github.com/kingosticks> Does mopidy know what is or isn't a stream at any point, or is that information lost after the backend extension? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1875?email_source=notifications&email_token=AAHEHKFO4UEU26FACCX74NTRAKD7BA5CNFSM4KM42TK2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEKKCMGQ#issuecomment-580134426>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAHEHKB5MR2SFXRSB5D5PUDRAKD7BANCNFSM4KM42TKQ> .

[leaty]

I figured. If we did that, I'm assuming extensions would have to start providing it for the ultimate fix to work. We could still allow them to function until they do though, by keeping this hack for a while. Anyway I approve this change.

[kingosticks]

I think we'd always want to reset the stream_title, before then deciding if we actually want to actually set it and emit the event (which we should only do when Track.is_stream). It's maybe less of a hack than it first looks!

[jodal]

👍 from me, but I'd like @adamcik to have a look too.

[adamcik]

I think this is OK, but would file a bug to followup. The bug might still get ignored, but less so than just a TODO.