avformat/rmdec: Fix DoS due to lack of eof check

Fixes: loop.ivr

Found-by: Xiaohei and Wangchu from Alibaba Security Team
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 124eb202)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rmdec.c

@@ -1235,8 +1235,11 @@ static int ivr_read_header(AVFormatContext *s)
             av_log(s, AV_LOG_DEBUG, "%s = '%s'\n", key, val);
         } else if (type == 4) {
             av_log(s, AV_LOG_DEBUG, "%s = '0x", key);
-            for (j = 0; j < len; j++)
+            for (j = 0; j < len; j++) {
+                if (avio_feof(pb))
+                    return AVERROR_INVALIDDATA;
                 av_log(s, AV_LOG_DEBUG, "%X", avio_r8(pb));
+            }
             av_log(s, AV_LOG_DEBUG, "'\n");
         } else if (len == 4 && type == 3 && !strncmp(key, "StreamCount", tlen)) {
             nb_streams = value = avio_rb32(pb);