AAC encoder: use signed coeffs when measuring IS energy

I/S energy, especially when it comes to phase cancellations,
needs to use signed coefficients as input, yet it was using
abs'd coefficients. That was a slight bug.

libavcodec/aacenc_is.c

@@ -120,8 +120,8 @@ void ff_aac_search_for_is(AACEncContext *s, AVCodecContext *avctx, ChannelElemen
                 struct AACISError ph_err1, ph_err2, *best;
                 for (w2 = 0; w2 < sce0->ics.group_len[w]; w2++) {
                     for (i = 0; i < sce0->ics.swb_sizes[g]; i++) {
-                        float coef0 = fabsf(sce0->coeffs[start+(w+w2)*128+i]);
-                        float coef1 = fabsf(sce1->coeffs[start+(w+w2)*128+i]);
+                        float coef0 = sce0->coeffs[start+(w+w2)*128+i];
+                        float coef1 = sce1->coeffs[start+(w+w2)*128+i];
                         ener0  += coef0*coef0;
                         ener1  += coef1*coef1;
                         ener01 += (coef0 + coef1)*(coef0 + coef1);

tests/fate/aac.mak

@@ -191,7 +191,7 @@ fate-aac-is-encode: CMD = enc_dec_pcm adts wav s16le $(TARGET_SAMPLES)/audio-ref
 fate-aac-is-encode: CMP = stddev
 fate-aac-is-encode: REF = $(SAMPLES)/audio-reference/luckynight_2ch_44kHz_s16.wav
 fate-aac-is-encode: CMP_SHIFT = -4096
-fate-aac-is-encode: CMP_TARGET = 597
+fate-aac-is-encode: CMP_TARGET = 615
 fate-aac-is-encode: SIZE_TOLERANCE = 3560
 fate-aac-is-encode: FUZZ = 10