avcodec/snappy: Sanity check bytestream2_get_levarint()

Fixes: left shift of 79 by 28 places cannot be represented in type 'int'
Fixes: 20202/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HAP_fuzzer-5719004081815552
Fixes: 20219/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HAP_fuzzer-5641738677125120
Fixes: 20389/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HAP_fuzzer-5680721517871104

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

libavcodec/snappy.c

@@ -39,6 +39,8 @@ static int64_t bytestream2_get_levarint(GetByteContext *gb)
 
     do {
         tmp = bytestream2_get_byte(gb);
+        if (shift > 31 || ((tmp & 127LL) << shift) > INT_MAX)
+            return AVERROR_INVALIDDATA;
         val |= (tmp & 127) << shift;
         shift += 7;
     } while (tmp & 128);