If the docked widgets in a QMainWindow grow larger than the screen, maximizing the MainWindow leads to glitches and overlapping in the docked widgets.

Steps to reproduce:

1. Install Qt 5.15 & run Qt Creator
2. Build & run the MainWindow example
3. Add dock widgets until the window is wider than the screen
4. Maximize the window
   1. Widgets now overlap
      
5. (Bonus) add another DockWidget
   1. The layout is now wider than Window and right side is out-of-screen