Mouse cursor is visible with captured mouse mode after window loses and regains focus.

[fabslab]

Godot version:
v3.0.6

OS/device including version:
Windows 10

Issue description:
Alt-tabbing with captured mouse mode results in mouse cursor becoming visible when it should remain hidden. Resetting the mouse mode once the window regains focus does not solve the issue either.

Steps to reproduce:
Create and run an autoload script with the following:

extends Node

func _ready():
	hide_mouse()

func _notification(event):
	if event == MainLoop.NOTIFICATION_WM_FOCUS_IN:
			hide_mouse()

func hide_mouse():
	Input.set_mouse_mode(Input.MOUSE_MODE_CAPTURED)

Alt-tab out of the game then back in and see that the mouse cursor is visible.

[ghost]

Confirmed on Windows 10.

@guilhermefelipecgs might know what's up.

@fabslab A work-around you can use for the time being:

func hide_mouse():
	Input.set_mouse_mode(Input.MOUSE_MODE_VISIBLE)
	Input.set_mouse_mode(Input.MOUSE_MODE_CAPTURED)

[RandomShaper]

I'm pretty sure I can fix this, so self-assigned.