4afa66fe41
When updating the main monitor, make sure to update the toplevel main monitor before trying to use that as the main monitor for non-toplevel windows (such as popups). Without this, when the main monitor is updated as a side effect to monitors being changed (for example due to a hot plug event, or coming back from being suspended) the main monitor pointer may, after 'monitors-changed' has completed, point to freed memory resulting in undefined behaviour. https://bugzilla.gnome.org/show_bug.cgi?id=784867