alsdec: make sure no invalid opt_order stays in the context.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/alsdec.c

@@ -664,6 +664,7 @@ static int read_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
                                                 2, sconf->max_order + 1));
             *bd->opt_order       = get_bits(gb, opt_order_length);
             if (*bd->opt_order > sconf->max_order) {
+                *bd->opt_order = sconf->max_order;
                 av_log(avctx, AV_LOG_ERROR, "Predictor order too large!\n");
                 return -1;
             }