MFH: r452524

x11-toolkits/nucleo: unbreak FFMPEG=on with Clang 4.0

ffmpegImageSink.cxx:246:29: error: ordered comparison between pointer and zero ('AVIOContext *' and 'int')

0, udp_callback, 0) < 0) {
~~~~~~~~~~~~~~~~~~~ ^ ~

Reported by: antoine (via bug 223057 exp-run)
Approved by: ports-secteam blanket