[X] Can't copy some unusual TRACK tags from MP3 / FLAC to WMA

[DetlevD]

@zerow

... I was using tag fields not in a "standard" way, with a bunch of signs different than just letters and numbers ... If the value in the TRACK tag field starts with a dot sign. I simply cannot copy such value to a WMA format. But if that dot was behind I number, then there would be no problem. Also if I have a letter or letters in the TRACK field, such value cannot be copy. But if letters are following a number, then there is no such problem. ...

Presumably Mp3tag does nothing else than the function $num() to verify and to get clean values for the tracknumber from user input.
At last the target filetype decides which datatype can be accepted.
Note: a dot character is not a number.

The Windows Media Format 11 SDK defines ...
WM/Track g_wszWMTrack WMT_TYPE_STRING
WM/TrackNumber g_wszWMTrackNumber WMT_TYPE_STRING
... and therefore it seems to be allowed, to store non numerical values into a WMA tag.

DD.20160306.1807.CET