In function process_output_surface(), the return value is 0 on the path
that av_mallocz() returns a NULL pointer. 0 indicates success, which
deviates from the fact. Return "AVERROR(ENOMEM)" instead of "0".
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>