Prevent duplicates in queue

[Shteevie]

I like to jump to an album to play in full when the first song of an album pops up in my radio feed.

However, I am already listening to the first song of the album, and the "add album to queue" function therefore adds a second copy of the first track to the queue.

In general, preventing duplicate songs from existing in the queue would make this flow easier and more successful.