streaming_extractor_music fails to get basename for file on Windows if path separators are backslashes

[phw]

If streaming_extractor_music gets called like this on Windows:

streaming_extractor_music.exe "C:\Users\Developer\Music\test.mp3" output.json

Then the file_name in the JSON will be "C:\\Users\\Developer\\Music\\test.mp3"

If streaming_extractor_music gets called with forward slashes it does extract the basename properly:

streaming_extractor_music.exe "C:/Users/Developer/Music/test.mp3" output.json

Here file_name is set to "test.mp3".

See also discussion at https://community.metabrainz.org/t/picard-submits-full-file-path-as-file-name-value-for-acousticbrainz-submission-bug/564530/3