Those strings has to be owned by mp_codec_params, not decoder wrapper
priv.
Our assumption is that we set those strings here once on decoder init
and they will not be changes during the life time of the
mp_codec_params, hence why we need to make sure they are not deallocated
too soon, in case they happen to be in use.
Fixes, use after free in some cases, when tracks are deselected.
Kacper Michajłow
24500c5e27