Cache directory results in FileScanner::searchForCoverFile
The cover lookup only depends on the directory, not the actual file name
So when scanning e.g. 100 files in the same directory we only need to check for the cover once, not 100 times
The cover lookup only depends on the directory, not the actual file name
So when scanning e.g. 100 files in the same directory we only need to check for the cover once, not 100 times