Line 78 needs to change to:
$client->execute(['playlist', 'addtracks', 'listRef', $items]);

The patch fixes the problem with the initial number of tracks in the playlist.

However, for each track finished playing, ten new tracks are added to the
playlist instead of just one new track. The number of tracks in the playlist
therefore grows towards infinity. This is probably not the intended behavior.

yup, just tested that myself.  use this instead:
$client->execute(['playlist', 'addtracks', 'listRef', $items]) unless $addOnly;

Fixed in subversion change 4141.