avformat/flvdec: Check for EOF in amf_skip_tag()

Fixes: Timeout
Fixes: 29070/clusterfuzz-testcase-minimized-ffmpeg_dem_KUX_fuzzer-5650106766458880

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 9725d07a17)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/flvdec.c

@@ -857,6 +857,9 @@ static int amf_skip_tag(AVIOContext *pb, AMFDataType type, int depth)
     if (depth > MAX_DEPTH)
         return AVERROR_PATCHWELCOME;
 
+    if (avio_feof(pb))
+        return AVERROR_EOF;
+
     switch (type) {
     case AMF_DATA_TYPE_NUMBER:
         avio_skip(pb, 8);