tools/zmqsend: use valid NULL log context

The zmq context is not a valid log context. Fix crash.
tools/zmqsend: rename ctx to zmq_ctx

The new name is more explicit.
wtv: make ff_format_videoinfo2 visible to wtv encoder

Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
wtvenc: use codec tag + MEDIASUBTYPE_BASE_GUID, if there is no suitable guid

This permits H264, AAC, AAC-LATM muxing.

Fixes ticket #536.

Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
wtvenc: output ff_format_none if ff_put_wav_header fails

This occurs when muxing E-AC-3.

Signed-off-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>