[regression] weston doesn't update screen if it was deactivating when a dialog was fading out, and it has been reactivated

Hi

I created this initially a few hours ago, but I was wrong about the commit that is the actual issue, the commit that seems to be causing the issue is actually a1f8c49d

It seems that now, if Weston is running, and it is deactivated when a window is being faded out, later attempts to reactivate it results in a non-responsive instance of Weston. (Well graphically unresponsive instance of Weston. It still responds to key commands, but the screen doesn't draw anymore)

In my instance, the window that is fading out is a kdialog menu that can start other instances of Weston, which makes catching this bug fairly easy

Nothing tasty appears to get logged in the log file, so no help there, but I did narrow it down to a1f8c49d

Setting close-animation=none seems to work around it, and if I switch from Weston when no fade animation is playing Weston doesn't hang there, just when the animation is running

Thanks