utils: Improve album title retrieval

A Grl.Media can be a container or a specific media item. In the latter case
if there was no album title tag, the fallback would be the filename. This
would result in two columns potentially having the same value in Songs
view.
Instead return "Unknown album" if the tag is not available.
4 jobs for wip/mschraal/utils-album-title-unknown in 10 minutes and 35 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Check
passed #260242
flake8

00:01:33

 
  Build Flatpak
passed #260243
flatpak

00:06:52

 
  Deploy
passed #260244
review

00:01:05

passed #260245
allowed to fail manual
stop_review

00:01:03