avcodec/takdsp: Fix negative shift in decorrelate_sf()

Fixes: left shift of negative value -4
Fixes: 25723/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_TAK_fuzzer-6250580752990208

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 4f54f53003)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/takdsp.c

@@ -65,7 +65,7 @@ static void decorrelate_sf(int32_t *p1, int32_t *p2, int length, int dshift, int
     for (i = 0; i < length; i++) {
         int32_t a = p1[i];
         int32_t b = p2[i];
-        b         = dfactor * (b >> dshift) + 128 >> 8 << dshift;
+        b         = (unsigned)(dfactor * (b >> dshift) + 128 >> 8) << dshift;
         p1[i]     = b - a;
     }
 }