Fix spurious redraw

m_last_setup was not storing the actual position that was used to
redraw the window, but the previous one, leading to an additional
spurious redraw immediatly after (triggered by window position not
believed to be the one at last redraw).

Fixes #2562

src/window.cc

@@ -170,8 +170,8 @@ const DisplayBuffer& Window::update_display_buffer(const Context& context)
 
     m_display_buffer.optimize();
 
-    m_last_setup = build_setup(context);
     set_position(setup.window_pos);
+    m_last_setup = build_setup(context);
 
     if (profile and not (buffer().flags() & Buffer::Flags::Debug))
     {