Tag guess: fallback on guessing if tag is empty

[naku]

After importing music, return tags parsed from the zip file
If tags are empty, fallback on pattern matching :
ex : 00 - Title.mp3
00 Title.mp3
00 Album - Title.mp3

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Do 2 passes.
1st pass:
Find 1st pattern that match all files, apply to all

2nd pass:
Find 1st pattern that match any file, apply to all

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