avcodec/utils: Remove always-true check

avcodec/utils: Remove always-true check

The first thing avcodec_open2() allocates is the AVCodecInternal. If
allocating it fails, a jump to end occurs; but if an error happens after
its allocation, a jump to free_and_end happens which frees all
allocations performed so far and then jumps to end. Yet free_and_end
contained a check for AVCodecInternal (after having already dereferenced
it to check whether ff_thread_free() needs to be called) which is of
course always true. So remove it.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>