MediaLibrary: Set logger before acquiring file lock

File locking will attempt to log on failure (ie: the medialib is already
locked).
As `s_logger` null checks were removed [1], logging before constructing
`MediaLibrary` was dereferencing nullptr.

[1] fc002ae1
8 jobs for !673 with fix/lock-file-crash in 7 minutes and 37 seconds (queued for 2 seconds)
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