avformat/vividas: Check for zero v_size

Fixes: SEGV on unknown address 0x000000000000
Fixes: 26482/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-4905102324006912

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

libavformat/vividas.c

@@ -679,7 +679,7 @@ static int viv_read_packet(AVFormatContext *s,
             return AVERROR_INVALIDDATA;
 
         ffio_read_varlen(pb);
-        if (v_size > INT_MAX)
+        if (v_size > INT_MAX || !v_size)
             return AVERROR_INVALIDDATA;
         ret = av_get_packet(pb, pkt, v_size);
         if (ret < 0)
@@ -708,7 +708,7 @@ static int viv_read_packet(AVFormatContext *s,
     } else {
         uint64_t v_size = ffio_read_varlen(pb);
 
-        if (v_size > INT_MAX)
+        if (v_size > INT_MAX || !v_size)
             return AVERROR_INVALIDDATA;
         ret = av_get_packet(pb, pkt, v_size);
         if (ret < 0)