avcodec/g723_1dec: fix invalid shift with negative sid_gain

Fixes: left shift of negative value -1
Fixes: 18395/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_G723_1_fuzzer-5710313034350592

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

libavcodec/g723_1dec.c

@@ -677,7 +677,7 @@ static int estimate_sid_gain(G723_1_ChannelContext *p)
             if (p->sid_gain < 0) t = INT32_MIN;
             else                 t = INT32_MAX;
         } else
-            t = p->sid_gain << shift;
+            t = p->sid_gain * (1 << shift);
     } else if(shift < -31) {
         t = (p->sid_gain < 0) ? -1 : 0;
     }else