dcaenc: fix out of array read

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/dcaenc.c

@@ -503,13 +503,13 @@ static int encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
     samples = (const int16_t *)frame->data[0];
     for (i = 0; i < PCM_SAMPLES; i ++) { /* i is the decimated sample number */
         for (channel = 0; channel < c->prim_channels + 1; channel++) {
+            real_channel = c->channel_order_tab[channel];
+            if (real_channel >= 0) {
                 /* Get 32 PCM samples */
                 for (k = 0; k < 32; k++) { /* k is the sample number in a 32-sample block */
                     c->pcm[k] = samples[avctx->channels * (32 * i + k) + channel] << 16;
                 }
                 /* Put subband samples into the proper place */
-            real_channel = c->channel_order_tab[channel];
-            if (real_channel >= 0) {
                 qmf_decompose(c, c->pcm, &c->subband[i][real_channel][0], real_channel);
             }
         }