avcodec/options: do a more thorough clean up in avcodec_copy_context()

Free coded_frame, coded_side_data and unref hw_device_ctx to prevent
potential leaks.

Reviewed-by: Aaron Levinson <alevinsn@aracnet.com>
Tested-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: James Almer <jamrial@gmail.com>
