avcodec/apedec: Fix undefined integer overflow in decode_array_0000()

Fixes: signed integer overflow: -2143289344 - 6246400 cannot be represented in type 'int'
Fixes: 19239/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5173755680915456

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

libavcodec/apedec.c

@@ -615,7 +615,7 @@ static void decode_array_0000(APEContext *ctx, GetBitContext *gb,
             return ;
         }
         out[i] = get_rice_ook(&ctx->gb, rice->k);
-        rice->ksum += out[i] - out[i - 64];
+        rice->ksum += out[i] - (unsigned)out[i - 64];
         while (rice->ksum < ksummin) {
             rice->k--;
             ksummin = rice->k ? ksummin >> 1 : 0;