Zero 'idx' for each iteration of the coupling gain loop and as it is only used

within this loop, we can move its declaration there too. This fixes bitstream
desync when decoding streams containing CCEs.

Based on a patch by Alex Converse (alex converse gmail com)

Originally committed as revision 15364 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/aac.c

@@ -950,7 +950,7 @@ static int decode_cpe(AACContext * ac, GetBitContext * gb, int elem_id) {
  */
 static int decode_cce(AACContext * ac, GetBitContext * gb, ChannelElement * che) {
     int num_gain = 0;
-    int c, g, sfb, ret, idx = 0;
+    int c, g, sfb, ret;
     int sign;
     float scale;
     SingleChannelElement * sce = &che->ch[0];
@@ -985,6 +985,7 @@ static int decode_cce(AACContext * ac, GetBitContext * gb, ChannelElement * che)
         return ret;
 
     for (c = 0; c < num_gain; c++) {
+        int idx = 0;
         int cge = 1;
         int gain = 0;
         float gain_cache = 1.;