getid3 doesn't work properly with the oc:// wrapper.

so use real path instead. With this change the database is filled with correct playtime values(existing entries need to be deleted). Attention: scanner won't scan non-local files with this fix. **That's not a real fix. Just to discuss this issue.**

https://github.com/owncloud/3rdparty/blob/master/getid3/module.audio.mp3.php#L1343 seems to be the function that doesn't work.