VLC tag editor breaks ID3v2 TRCK frame

TPOS frame can be written in "current/total" format.

VLC splits TRCK on reading, but doesn't join "total" part back on writing. Instead, TrackTotal is written as TXXX:TRACKTOTAL frame.

Moreover, before this, it uses setTrack from taglib to set the current track number. The method accepts an integer, so the "total" part always removed from the original TRCK.