Fix regression in r1232 which caused silent playback on 10.4.
Fix regression in r1232 which caused silent playback on 10.4.

NULL magic cookie means "don't change it", not "delete extradata".

Additionally, call avcodec_get_context_defaults2() in the constructor
rather than in OpenAVCodec, since it overwrites the old extradata and made
r1232 ineffective.


git-svn-id: d8f21eb7283bfb39ebab2f8f9b4a259b233f9348@1236 621663c8-3916-0410-8f58-edc14a8543d5

mrvacbob/perian,mrvacbob/perian,mrvacbob/perian,mrvacbob/perian,mrvacbob/perian