Fix an enc/dec mismatch issue in tokenization

Resolve an enc/dec mismatch issue in new-tokenset and var-tx.

BUG=aomedia:567

Change-Id: I9bd8ec4c7716bca3a5e551b6e9838fc8ef37f198

av1/encoder/bitstream.c

@@ -855,6 +855,9 @@ static void pack_mb_tokens(aom_writer *w, const TOKENEXTRA **tp,
     if (token == BLOCK_Z_TOKEN) {
       aom_write_symbol(w, 0, *p->head_cdf, HEAD_TOKENS + 1);
       p++;
+#if CONFIG_VAR_TX
+      break;
+#endif
       continue;
     }