artistalbumswidget: Wait for last album to load

Since album widget population is async, it's not guaranteed that
the last album in the list will load last. In particular, this
can happen if the last album is small, and next to last album is
large.

Fixes #174


(cherry picked from commit 761b7041)
3 jobs for cherry-pick-761b7041 in 6 minutes and 5 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Check
passed pep8 #30733

00:02:38

passed pyflakes #30732

00:01:18

 
  Build
passed build #30734

00:03:13