aacenc: reset marked IS and M/S bands upon frame encoding

This commit resets any bands marked as M/S or IS upon encoding a frame.
This is needed because the arrays may contain some residual information
upon allocation on startup and because there isn't any mechanism to
reset the arrays once the frame has been encoded.
Reviewed-by: Claudio Freire <klaussfreire@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/aacenc.c

@@ -617,6 +617,8 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
             tag      = s->chan_map[i+1];
             chans    = tag == TYPE_CPE ? 2 : 1;
             cpe      = &s->cpe[i];
+            memset(cpe->is_mask, 0, sizeof(cpe->is_mask));
+            memset(cpe->ms_mask, 0, sizeof(cpe->ms_mask));
             put_bits(&s->pb, 3, tag);
             put_bits(&s->pb, 4, chan_el_counter[tag]++);
             for (ch = 0; ch < chans; ch++)