some work in morm (select statement)

git-svn-id: svn://ttmath.org/publicrep/morm/trunk@1079 e52654a7-88a9-db11-a3e9-0013d4bc506e

src/baseexpression.cpp

@@ -67,6 +67,8 @@ void BaseExpression::generate_from_model(PT::TextStream & stream, Model & model)
 	before_generate_from_model();
 	model.map_fields();
 	after_generate_from_model();
+
+	this->out_stream = nullptr;
 }