### Description
It is good to have a deterministic order when doing explicit file
sorting. This sorts by filename when last played time is null. I would
expect filename to be the next sort after last played time in case of a
tie, and was surprised to find it was not explicit. It should not break
any existing use cases.
**This is a new feature**:
Kind of?
**I have updated the documentation to reflect these changes**:
I did not update any documentation as this way seems like the logical
expected way to do the sort.
### Testing Notes
**What I did:**
I loaded up some tracks into a local libretime instance, let some of
them play, and tested that all the old sorts worked as before as well as
tracks getting sorted by filepath in case of a last played time
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