Disappearing Window Related to Fullscreening

@poush observed in testing that it was possible to full screen H2, access another window and press Esc, and then lose the H2 window.

I was unable to re-produce on Ubuntu 18.04 or Windows 10, so this potentially may be a bug with Mac specifically. This may also be fixed now by the "Esc" shortcut being converted to a local shortcut, but documenting in the event this issue still persists for some users.

[poush]

To reproduce:

1. Start H2 from the master branch
2. Make it full screen
3. Change to different screen
4. Press Esc and now H2 screen is lost. All you can do to bring it back is press the full-screen keys again and then exit full screen being on the same screen in which h2 is running.