check norm6 vlc validity as there are some bit sequences which dont corespond to any codeword, the other vlc tables all seem to be huffman tables though

Originally committed as revision 3883 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/vc9.c

@@ -852,6 +852,10 @@ static int bitplane_decoding(BitPlane *bp, VC9Context *v)
         for(y=  bp->height%tile_h; y< bp->height; y+=tile_h){
             for(x=  bp->width%tile_w; x< bp->width; x+=tile_w){
                 code = get_vlc2(&v->gb, vc9_norm6_vlc.table, VC9_NORM6_VLC_BITS, 2);
+                if(code<0){
+                    av_log(v->avctx, AV_LOG_DEBUG, "inavlid NORM-6 VLC\n");
+                    return -1;
+                }
                 //FIXME following is a pure guess and probably wrong
                 //FIXME A bitplane (0 | !0), so could the shifts be avoided ?
                 planep[x     + 0*bp->stride]= (code>>0)&1;