form line: add constructor without lvobj

radio/src/thirdparty/libopenui/src/form.cpp

@@ -73,6 +73,12 @@ FormGroup::Line::Line(Window* parent, lv_obj_t* obj, FlexGridLayout* layout) :
   construct();
 }
 
+FormGroup::Line::Line(Window* parent, FlexGridLayout* layout) :
+    Window(parent, rect_t{}), layout(layout)
+{
+  construct();
+}
+
 void FormGroup::Line::construct()
 {
   // forward scroll and focus

radio/src/thirdparty/libopenui/src/form.h

@@ -88,6 +88,7 @@ class FormGroup : public Window
 
    public:
     Line(Window *parent, lv_obj_t *obj, FlexGridLayout *layout = nullptr);
+    Line(Window *parent, FlexGridLayout *layout = nullptr);
 
    protected:
     void addChild(Window *window) override;