[0.16.4] Mouse Leaving Screen removes selection box

[Mobius1]

Bug Report:
What's the issue?
Mouse cursor leaving game screen removes selection box of entities when we move it back.

How can we reproduce it?
Tested it in 3 types of situations:
- Factorio in fullscreen mode with dual monitors
- Factorio in windowed mode
- Factorio in windowed mode with dual monitors

On the first test subject, whenever we alt-tab out of the game or just move the mouse to the other screen, the selection box of everything in the game gets lost, it doesn't show up, so we can't interact with anything, but keyboard still works
On the second test subject, with factorio in windowed mode, whenever we move the mouse to the title of the screen, or the taskbar the selection box flees again, but this time we can workaround by changing the size of the screen, when the window finishes resizing with the mouse inside the game window, the selection box appears again.
On the 3rd test subject, when the mouse leaves the screen to hit the other monitor, the selection box fades again but we can recover it by resizing the game window.

All of the testing above was done in the version 0.16.4 of the game, computer settings haven't change since last working version (0.15.40).
On 0.15.40 the issues reported above were absent from the game.

[sylan0]

Thank you, more comprehensive test than I would've thought of as I just experienced that you can't interact with anything mouse related. First legitimately thought I'd stopped playing for so long the mouse had been changed to no longer perform mining and started playing with keys to do the basics, but am experiencing the same thing on the same build. After restarting a few times game I only noticed after alt tabbing that it disappears.