avformat/rmdec: Fix EOF check in the stream loop in ivr_read_header()

Fixes: long running loop
Fixes: ivr-timeout-42468cb797f52f025fb329394702f5d4d64322d6

Found-by: Paul Ch <paulcher@icloud.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit c2eec1762d)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rmdec.c

@@ -1270,6 +1270,8 @@ static int ivr_read_header(AVFormatContext *s)
                 if (avio_rb32(pb) == MKBETAG('M', 'L', 'T', 'I')) {
                     ret = rm_read_multi(s, pb, st, NULL);
                 } else {
+                    if (avio_feof(pb))
+                        return AVERROR_INVALIDDATA;
                     avio_seek(pb, -4, SEEK_CUR);
                     ret = ff_rm_read_mdpr_codecdata(s, pb, st, st->priv_data, len, NULL);
                 }