Black screen when slide up application on iphone

[Hyhyx]

Describe the bug:

Black screen when slide up application on iphone

To Reproduce:

Steps to reproduce the behaviour:

1. fyne release ios ... (use development certificate)
2. ideviceinstaller -i FyneIos.ipa
3. open the application
4. slide up from the bottom

Screenshots:

Example code:

package main

import (
	"fyne.io/fyne/app"
	"fyne.io/fyne/widget"
)

func main() {
	a := app.New()
	w := a.NewWindow("Hello")

	hello := widget.NewLabel("Hello Fyne!")
	w.SetContent(widget.NewVBox(
		hello,
		widget.NewButton("Hi!", func() {
			hello.SetText("Welcome :)")
		}),
	))

	w.ShowAndRun()
}

Device (please complete the following information):

• OS: iOS
• Version: 14.0
• Go version: 1.15
• Fyne version: 1.4.1

[andydotxyz]

Thanks for capturing the bug, you're quite right I see it to.
I thought this was an intermittent bug but it's not.
If the app contains animations it will work OK - so it seems to relate to the driver missing a refresh as the app goes into background. We should resolve this!

[andydotxyz]

Fix is on develop ready for release