04205039f24ea6e71d2ce94c7cb7e1395f95179e was not enough to
fix the ordered list issue introduced by
26f0033ebb5f8e7c204a042709e3dfa885eac868.
heap.Pop uses Swap internally which modifies as songs index.

We fix the broken indices by overriding them after the ordered list
was created.

Storing song objects in the Songs slice and using pointers to the
underlying array slots breaks if the underlying array must be grown.
When the array is grown the objects are copied to the new array and
the pointers used in queue point to the old objects.
This causes that Playlist.applyTimeBonus may not correctly apply
to the most recent list of songs.

This is fixed by always using Song pointers.

This ensures that the initial reported song array is in order.