[Merge] ~vanvugt/ubuntu/+source/mutter:fix-lp1847551 into ~ubuntu-desktop/ubuntu/+source/mutter:ubuntu/master

[Iain Lane]

Review: Disapprove

Thanks, but since Marco (probably prompted by discussing this bug, so it wasn't wasted) proposed taking the whole gnome-3-34 branch up until yesterday, which will include this same fix we won't need a separate upload. 
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https://code.launchpad.net/~vanvugt/ubuntu/+source/mutter/+git/mutter/+merge/374507
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