avcodec/sonic: Fix several integer overflows

Fixes: signed integer overflow: 2129689466 + 2129689466 cannot be represented in type 'int'
Fixes: 20715/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SONIC_fuzzer-5155263109922816

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 75d520e337)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/sonic.c

@@ -140,7 +140,8 @@ static inline av_flatten int get_symbol(RangeCoder *c, uint8_t *state, int is_si
     if(get_rac(c, state+0))
         return 0;
     else{
-        int i, e, a;
+        int i, e;
+        unsigned a;
         e= 0;
         while(get_rac(c, state+1 + FFMIN(e,9))){ //1..10
             e++;
@@ -474,7 +475,7 @@ static int predictor_calc_error(int *k, int *state, int order, int error)
     for (i = order-2; i >= 0; i--, k_ptr--, state_ptr--)
     {
         int k_value = *k_ptr, state_value = *state_ptr;
-        x -= shift_down(k_value * state_value, LATTICE_SHIFT);
+        x -= shift_down(k_value * (unsigned)state_value, LATTICE_SHIFT);
         state_ptr[1] = state_value + shift_down(k_value * (unsigned)x, LATTICE_SHIFT);
     }
 #else
@@ -1044,7 +1045,7 @@ static int sonic_decode_frame(AVCodecContext *avctx,
                 x += s->channels;
             }
 
-            s->int_samples[x] = predictor_calc_error(s->predictor_k, s->predictor_state[ch], s->num_taps, s->coded_samples[ch][i] * quant);
+            s->int_samples[x] = predictor_calc_error(s->predictor_k, s->predictor_state[ch], s->num_taps, s->coded_samples[ch][i] * (unsigned)quant);
             x += s->channels;
         }