Fix checkCodec() call

[rkfg]

I have no idea why this compiles in GCC 5 and 6 in the first place (maybe this constructor is not used anywhere), but GCC 7 fails with this error:

In file included from /home/rkfg/soft/avcpp/src/codeccontext.cpp:7:0:
/home/rkfg/soft/avcpp/src/codeccontext.h: In constructor ‘av::CodecContextBase<Clazz, _direction, _type>::CodecContextBase(const av::Codec&)’:
/home/rkfg/soft/avcpp/src/codeccontext.h:313:39: error: no matching function for call to ‘av::CodecContextBase<Clazz, _direction, _type>::checkCodec(const av::Codec&, av::OptionalErrorCode)’
         if (checkCodec(codec, throws()))
                                       ^
/home/rkfg/soft/avcpp/src/codeccontext.h:132:10: note: candidate: bool av::CodecContext2::checkCodec(const av::Codec&, av::Direction, AVMediaType, av::OptionalErrorCode)
     bool checkCodec(const Codec& codec, Direction direction, AVMediaType type, OptionalErrorCode ec);
          ^~~~~~~~~~
/home/rkfg/soft/avcpp/src/codeccontext.h:132:10: note:   candidate expects 4 arguments, 2 provided

[h4tr3d]

Codec must be compatible with CodecContext, so it is incorrect to pass direction and type info taken from the codec itself. Just use _direction and _type template parameters as a function argument:

if (checkCodec(codec, _direction, _type, throws()))

[rkfg]

Should be good now.

[h4tr3d]

Thanks a lot!