avcodec/sonic: Check e in get_symbol()

Fixes: signed integer overflow: 1721520852 + 1721520852 cannot be represented in type 'int'
Fixes: 18346/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SONIC_fuzzer-5709623893426176
Fixes: 18753/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SONIC_fuzzer-5663299131932672

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

libavcodec/sonic.c

@@ -144,6 +144,8 @@ static inline av_flatten int get_symbol(RangeCoder *c, uint8_t *state, int is_si
         e= 0;
         while(get_rac(c, state+1 + FFMIN(e,9))){ //1..10
             e++;
+            if (e > 31)
+                return AVERROR_INVALIDDATA;
         }
 
         a= 1;