ac3dec: fix outptr increment.

Fixes corrupt data errors when downmixing in the AC-3 decoder.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Justin Ruggles <justin.ruggles@gmail.com>

CC:libav-stable@libav.org

libavcodec/ac3dec.c

@@ -1400,7 +1400,7 @@ static int ac3_decode_frame(AVCodecContext * avctx, void *data,
                 memcpy(s->outptr[channel_map[ch]], output[ch], sizeof(**output) * AC3_BLOCK_SIZE);
         for (ch = 0; ch < s->out_channels; ch++)
             output[ch] = s->outptr[channel_map[ch]];
-        for (ch = 0; ch < s->channels; ch++)
+        for (ch = 0; ch < s->out_channels; ch++)
             s->outptr[ch] += AC3_BLOCK_SIZE;
     }