avcodec/dca: clear X96 channels if nothing was decoded

The first X96 channel set can have more channels than core, causing X96
decoding to be skipped. Clear the number of decoded X96 channels to zero
in this rudimentary case.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/dca_core.c

@@ -1760,6 +1760,7 @@ static int parse_x96_frame_exss(DCACoreDecoder *s)
         return ret;
 
     // Channel set data
+    s->x96_nchannels = 0;
     for (i = 0, x96_base_ch = 0; i < x96_nchsets; i++) {
         header_pos = get_bits_count(&s->gb);