avcodec/g723_1dec: Fix overflow in shift

Fixes: shift exponent 1008 is too large for 32-bit type 'int'
Fixes: 17700/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_G723_1_fuzzer-5707633436131328

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

libavcodec/g723_1dec.c

@@ -678,6 +678,8 @@ static int estimate_sid_gain(G723_1_ChannelContext *p)
             else                 t = INT32_MAX;
         } else
             t = p->sid_gain << shift;
+    } else if(shift < -31) {
+        t = (p->sid_gain < 0) ? -1 : 0;
     }else
         t = p->sid_gain >> -shift;
     x = av_clipl_int32(t * (int64_t)cng_filt[0] >> 16);