Should fix a crash reported by the bugreport ml.

audioscrobbler: *Never* do module unloading from within the module. You are basically unloading the code you are executing, that's a nice crasher.

Also make sure playlist is not NULL. (This is an attempt to fix a from the famous bugreport ml).

The audio output locking rule seems very vague. Moreover there could be some cross lock issues.

Spotted in our bugreport ml.

The check was stupid (always was). This seems way more logical.

- This is REALLY slow.
- It is slow each time you Seek to somewhere that you have not been/played before.
- We ought to create a "Repair index" function instead, like for avi. (no time before release)

This close ticket #1687