avformat/vividas: Check avio_read() for failure

Fixes: use of uninitialized value (untested)
Fixes: 42537627/clusterfuzz-testcase-minimized-fuzzer_loadfile_direct-5505802505355264

Found-by: ossfuzz
Reported-by: Kacper Michajlow
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/vividas.c

@@ -567,7 +567,8 @@ static int viv_read_header(AVFormatContext *s)
     v = avio_r8(pb);
     avio_seek(pb, v, SEEK_CUR);
 
-    avio_read(pb, keybuffer, 187);
+    if (avio_read(pb, keybuffer, 187) != 187)
+        return AVERROR_INVALIDDATA;
     key = decode_key(keybuffer);
     viv->sb_key = key;