Reported by Matthew Woehlke, debugged by myself, fix identified by Piotr
Figiel.

In essence, Q3ListItemView uses an int id to identify each column. JuK
supports some playlists having additional columns, which is why you see
references to "offset" scattered throughout the playlist-column-handling
code.

In this case, our "maximum column id" value is itself a valid column ID,
so Piotr is entirely correct in fixing the check here. I have recompiled
and retested and sorting by the Full Path playlist column now works
properly. Thanks to everyone involved in getting this ancient bug
stamped out.

BUG:307649
FIXED-IN:4.9.3