r29348 changes can cause certain codecs to jump to code on early track change that...

r29348 changes can cause certain codecs to jump to code on early track change that assumes initializations have been done. Make sure that track change cleanups are only called if the state is sane to do so. Stops my vorbis data abort issue. Correctness for speex is a guess based on the library calls' source. It appears only speex/vorbis should have been bothered by said revision.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29489 a1c6a512-1295-4272-9138-f99709370657