avcodec/apedec: Use NABS to avoid undefined negation

Fixes: negation of -2147483648 cannot be represented in type 'int32_t' (aka 'int'); cast to an unsigned type to negate this value to itself
Fixes: 67738/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5444313212321792

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

@@ -1287,7 +1287,7 @@ static void predictor_decode_stereo_3950(APEContext *ctx, int count)
                 int32_t left  = a1 - (unsigned)(a0 / 2);
                 int32_t right = left + (unsigned)a0;
 
-                if (FFMAX(FFABS(left), FFABS(right)) > (1<<23)) {
+                if (FFMIN(FFNABS(left), FFNABS(right)) < -(1<<23)) {
                     ctx->interim_mode = !interim_mode;
                     av_log(ctx->avctx, AV_LOG_VERBOSE, "Interim mode: %d\n", ctx->interim_mode);
                     break;