Fix reload embedded cover

I figured out what is the bug that jus is seeing. The 'changeCover' function is still not checking if the coverLocation is set to ID3TAG. Then of course the loaded image will be null and the change fails. It would be an easy enough change but I want to have a test for this first.

But that is not as easy as I thought. The test I added always segfaults at line 105 and I have no clue why.