Fallback art is displayed in the toolbar and Now Playing view sometimes when the art is actually defined

[Victor Thompson]

The thumbnailer service now allows the app to catch and display custom fallback art. This seems to work well, but the artwork displayed in the toolbar and the Now Playing Full View sometimes incorrectly display the fallback artwork.

To reproduce:

1. Play any album with valid artwork.
2. Close the now playing view.
3. Note that the artwork in the toolbar is correct.
4. Play any album with INVALID artwork (the fallback art is shown)
5. Close the now playing view.
6. Note that the artwork in the toolbar is the fallback image.
7. Tap the toolbar, select the Queue, and clear it (this step is optional)
8. Play any album with valid artwork.
9. Close the now playing view.
10. Note that the artwork in the toolbar is incorrect (the fallback art is shown).

Expected results: Step #10 should show the correct artwork
Actual results: Step #10 shows the fallback artwork.

The log data seems to suggest that the artwork being requested is still the songs/album from Step #4.

[Jenkins Bot (ubuntu-core-apps-jenkins-bot)]

Fix committed into lp:music-app at revision 995, scheduled for release in music-app, milestone ota10