avformat/hlsenc: Fix return value from localtime_r failure

"If an error is detected, localtime_r() shall return a null pointer
and set errno to indicate the error." Yet in case this happened in
hls_init(), AVERROR(ENOMEM) has been returned.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Reviewed-by: Steven Liu <lq@onvideo.cn>

libavformat/hlsenc.c

@@ -2737,7 +2737,7 @@ static int hls_init(AVFormatContext *s)
             char b[15];
             struct tm *p, tmbuf;
             if (!(p = localtime_r(&t, &tmbuf)))
-                return AVERROR(ENOMEM);
+                return AVERROR(errno);
             if (!strftime(b, sizeof(b), "%Y%m%d%H%M%S", p))
                 return AVERROR(ENOMEM);
             hls->start_sequence = strtoll(b, NULL, 10);