Call ProcessScheduledResize from FinishInitNested

This is to make sure that OnResize is called at least once before
the window is first drawn, to set up scrollbar capacities, etc

See: d3c673e2

src/window.cpp

@@ -1871,6 +1871,7 @@ void Window::FinishInitNested(WindowNumber window_number)
 	Point pt = this->OnInitialPosition(this->nested_root->smallest_x, this->nested_root->smallest_y, window_number);
 	this->InitializePositionSize(pt.x, pt.y, this->nested_root->smallest_x, this->nested_root->smallest_y);
 	this->FindWindowPlacementAndResize(this->window_desc->GetDefaultWidth(), this->window_desc->GetDefaultHeight());
+	this->ProcessScheduledResize();
 }
 
 /**