1345: Auto-Tag from FileN Disc# not tagged if number [#7245]

[buskbolurven]

When making a auto tag from filename, the <Disc#> won't be tagged if it not is a number, but the field is alphanumerical, so it would be convenient if the auto tag also could accept alphanumerical values.

[Lowlander]

I see the same here. Added as: http://www.ventismedia.com/mantis/view.php?id=7245