small revert

sql/sql_base.cc

@@ -1078,7 +1078,7 @@ TABLE *open_table(THD *thd,const char *db,const char *table_name,
   table->status=STATUS_NO_RECORD;
   table->keys_in_use_for_query= table->keys_in_use;
   table->used_keys= table->keys_for_keyread;
-//   DBUG_ASSERT(table->key_read == 0); put in comment as this fails  on EXPLAIN
+  DBUG_ASSERT(table->key_read == 0);
   DBUG_RETURN(table);
 }