Fix some crashes, overflows and using variables without values

modules/visual_script/visual_script.cpp

@@ -1361,6 +1361,7 @@ void VisualScript::_bind_methods() {
 VisualScript::VisualScript() {
 
 	base_type = "Object";
+	is_tool_script = false;
 }
 
 StringName VisualScript::get_default_func() const {