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

Fix compilation warnings (here the lib might have ask for const char* instead of char as they don't modify the string at all)