Update plugin.c

Fix issue where manually switching tracks doesn't work.
Fix issue where seeking works, but automatically moves the position marker to the beginning of the track.
Update plugin.c

Adjusted for Audacious 3.3+
Merge pull request #2 from jmesick/master

Bug fixes - Thanks to jmesick
- Fix issue where manually switching tracks doesn't work.
- Fix issue where seeking works, but automatically moves the position marker to the beginning of the track.