Fix problem to fail by a RTMP Control Message except "Set Chunk Size (1)" after an RTMP handshake. When 'nginx-rtmp-module' relays an RTMP, it sends not only control message 'Set Chunk Size (1)' but also 'Window Acknowledgement Size (5)'.
Reviewed-by: Steven Liu <lingjiujianke@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>