Encode the Filepath utf-8

The filepath of a track gets broken when it contains special
UTF-8-characters. Encoding it UTF-8 fixes this behaviour.

api/funkwhale_api/music/views.py

@@ -230,7 +230,7 @@ def get_file_path(audio_file):
                     'MUSIC_DIRECTORY_PATH to serve in-place imported files'
                 )
             path = '/music' + audio_file.replace(prefix, '', 1)
-        return settings.PROTECT_FILES_PATH + path
+        return (settings.PROTECT_FILES_PATH + path).encode('utf-8')
     if t == 'apache2':
         try:
             path = audio_file.path