Per-Monitor Aware: Does not pick up DPI if started on a monitor with different DPI

[wizzard0]

Repro:
0. Win10 1709, VS2017, .NET 4.7.1

1. Have 2 monitors, with DPI 96 and 192 (for example). I use Surface Book + regular monitor
2. Set "Second screen only", logoff, login again, have system DPI at 96
3. Switch to "PC Screen only"
4. Open PerMonitorDemo.sln, confirm that Visual Studio uses raster scaling at this point.
5. Start app, Observe controls messed up.
   5.1. If you switch monitors to "Extend", the DPIChanged message arrives, and the app rescales properly.