avcodec/sonic: Fix two undefined integer overflows

Fixes: signed integer overflow: 2147483372 - -148624 cannot be represented in type 'int'
Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SONIC_fuzzer-5477177805373440
Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SONIC_fuzzer-6681622236233728

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 void predictor_init_state(int *k, int *state, int order)
 
 static int predictor_calc_error(int *k, int *state, int order, int error)
 {
-    int i, x = error - shift_down(k[order-1] *  (unsigned)state[order-1], LATTICE_SHIFT);
+    int i, x = error - (unsigned)shift_down(k[order-1] *  (unsigned)state[order-1], LATTICE_SHIFT);
 
 #if 1
     int *k_ptr = &(k[order-2]),
@@ -1013,7 +1013,7 @@ static int sonic_decode_frame(AVCodecContext *avctx, AVFrame *frame,
     if (s->lossless)
         quant = 1;
     else
-        quant = get_symbol(&c, state, 0) * SAMPLE_FACTOR;
+        quant = get_symbol(&c, state, 0) * (unsigned)SAMPLE_FACTOR;
 
 //    av_log(NULL, AV_LOG_INFO, "quant: %d\n", quant);