avformat/rmdec: Check remaining space in debug av_log() loop

Fixes: Timeout (long -> 2 ms)
Fixes: 26709/clusterfuzz-testcase-minimized-ffmpeg_dem_IVR_fuzzer-5665833403285504
Fixes: 27522/clusterfuzz-testcase-minimized-ffmpeg_dem_IVR_fuzzer-6321071221112832

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rmdec.c

@@ -1290,8 +1290,11 @@ static int ivr_read_header(AVFormatContext *s)
                 int j;
 
                 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, "Duration", tlen)) {
                 st->duration = avio_rb32(pb);