avcodec/apac: use unsigned for sample residual

Fixes: signed integer overflow: -2146670226 + -2227242 cannot be represented in type 'int'
Fixes: 51943/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APAC_fuzzer-5779018251370496

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/apac.c

@@ -208,7 +208,7 @@ static int apac_decode(AVCodecContext *avctx, AVFrame *frame,
 
             for (int i = 0; i < c->block_length; i++) {
                 int val = get_bits_long(gb, c->bit_length);
-                int delta = (val & 1) ? ~(val >> 1) : (val >> 1);
+                unsigned delta = (val & 1) ? ~(val >> 1) : (val >> 1);
                 int sample;
 
                 delta += c->last_delta;