avcodec/sonic: Fix integer overflow in predictor_calc_error()

Fixes: signed integer overflow: 5 * -1094995529 cannot be represented in type 'int'
Fixes: 18346/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SONIC_fuzzer-5709623893426176

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

@@ -473,7 +473,7 @@ static int predictor_calc_error(int *k, int *state, int order, int error)
     {
         int k_value = *k_ptr, state_value = *state_ptr;
         x -= shift_down(k_value * state_value, LATTICE_SHIFT);
-        state_ptr[1] = state_value + shift_down(k_value * x, LATTICE_SHIFT);
+        state_ptr[1] = state_value + shift_down(k_value * (unsigned)x, LATTICE_SHIFT);
     }
 #else
     for (i = order-2; i >= 0; i--)