lavf/{srt,microdvd}: correctly raise error on avformat_new_stream() error.

libavformat/microdvddec.c

@@ -62,7 +62,7 @@ static int microdvd_read_header(AVFormatContext *s)
     char c;
 
     if (!st)
-        return -1;
+        return AVERROR(ENOMEM);
     for (i=0; i<FF_ARRAY_ELEMS(microdvd->lines); i++) {
         microdvd->pos[i] = avio_tell(s->pb);
         ff_get_line(s->pb, microdvd->lines[i], sizeof(microdvd->lines[i]));

libavformat/srtdec.c

@@ -44,7 +44,7 @@ static int srt_read_header(AVFormatContext *s)
 {
     AVStream *st = avformat_new_stream(s, NULL);
     if (!st)
-        return -1;
+        return AVERROR(ENOMEM);
     avpriv_set_pts_info(st, 64, 1, 1000);
     st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;
     st->codec->codec_id   = CODEC_ID_SRT;