avcodec/takdec: Fix integer overflow in decode_lpc()

Fixes: runtime error: signed integer overflow: 16748560 + 2143729712 cannot be represented in type 'int'
Fixes: 3202/clusterfuzz-testcase-minimized-4988291642294272

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 5d31f03a02)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/takdec.c

@@ -206,7 +206,7 @@ static void decode_lpc(int32_t *coeffs, int mode, int length)
         int a1 = *coeffs++;
         for (i = 0; i < length - 1 >> 1; i++) {
             *coeffs   += a1;
-            coeffs[1] += *coeffs;
+            coeffs[1] += (unsigned)*coeffs;
             a1         = coeffs[1];
             coeffs    += 2;
         }