How to reproduce:
1. Create new project
2. When opened click the title bar of the main window
3. Press CTRL+N and notice that there is no new scene created
4. Click CTRL+S (nothing happens), give focus on the Inspector and press CTRL+S
5. When the Save Scene dialog shows up, close it without saving the Scene
6. Click CTRL+S (nothing happens again)

Expected: CTRL+N should create a new scene even without a focus on the Editor and CTRL+S should open the Save Scene dialog every time after pressing it, if the Scene is not saved
Actual: CTRL+N doesn't create a new scene without a focus on the Editor and CTRL+S doesn't open the Save Scene dialog every time after pressing it, if the Scene is not saved

Reproduced on: 2018.3.0a6, 2018.3.0a8
Not reproduced on: 2017.1.5f1, 2017.2.3p3, 2017.4.9f1, 2018.1.9f1, 2018.2.3f1, 2018.3.0a5

Note: The issue occurs only on Windows