test: Add non-existing item to playlist tests
test: Add non-existing item to playlist tests

jackwilsdon/beets,beetbox/beets,ibmibmibm/beets,sampsyo/beets,beetbox/beets,shamangeorge/beets,shamangeorge/beets,SusannaMaria/beets,beetbox/beets,sampsyo/beets,ibmibmibm/beets,jackwilsdon/beets,beetbox/beets,jackwilsdon/beets,sampsyo/beets,SusannaMaria/beets,sampsyo/beets,SusannaMaria/beets,ibmibmibm/beets,ibmibmibm/beets,shamangeorge/beets,shamangeorge/beets,SusannaMaria/beets,jackwilsdon/beets