[macOS] Screen::grabWindow() crashes in certain multiscreen scenarios

Steps to reproduce the issue:
1. Setup two screens from System Preferences so that the secondary screen is on top of the primary screen or so that the secondary screen is on the left side of primary screen. (See screenshot for details)
2. Run attached test application and make sure it's on the primary screen.
3. Click on the 'Capture Screen' button.

Outcome:
The application crashes

Notes:
The crash occurs only when x or y is 0 when passed to grabWindow(). Changing x or y to e.g. 1 will not crash the application anymore. This can be done either in user application or in qcocoaintegration.mm:276

Tested on:
macOS Sierra 10.12