refs #6195, fix bug in add index where bf_info->key_to_compare was not set

git-svn-id: file:///svn/mysql/tokudb-engine/tokudb-engine@54295 c7de825b-a66e-492c-adef-691d508d4ae1

storage/tokudb/ha_tokudb.cc

@@ -7761,6 +7761,7 @@ int ha_tokudb::tokudb_add_index(
         bf_info.direction = 1;
         bf_info.thd = ha_thd();
         bf_info.need_val = true;
+        bf_info.key_to_compare = NULL;
 
         error = db_env->create_loader(
             db_env,