avformat/vividas: Fix infinite loop in header parser

Fixes: Timeout (Infinite -> Finite)
Fixes: 16010/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5638616102993920

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

libavformat/vividas.c

@@ -546,6 +546,9 @@ static int viv_read_header(AVFormatContext *s)
             break;
 
         block_len = ffio_read_varlen(pb);
+        if (avio_feof(pb))
+            return AVERROR_INVALIDDATA;
+
         block_type = avio_r8(pb);
 
         if (block_type == 22) {