Having “on_all_workspaces_requested” FALSE on a window does not imply a
workspace is set.
If the X11 window is placed on a secondary monitor while workspaces
applies on primary monitor only (“workspaces-only-on-primary” set) then
“on_all_workspaces_requested” is FALSE while “on_all_workspaces“ is TRUE
and the associated workspace is NULL, leading to a crash when saving the
gnome-shell/mutter session.
So if no workspace is set, use the “initial_workspace” instead to avoid
a NULL pointer dereference.
https://bugzilla.gnome.org/show_bug.cgi?id=792818
We previously separated out MetaDisplay and MetaScreen. mutter
would only manage one screen, but we still kept a list of screens
for simplicity.
With Wayland support, we no longer care about the ability to
manage more than one screen at a time. Remove this by killing
the list of screens, in favor of having just one MetaScreen
in MetaDisplay.
We also kill off active_screen at the same time, since it's
not necessary anymore.
A future cleanup should merge MetaDisplay and MetaScreen. To avoid
breaking API, we should probably keep MetaScreen around as a dummy
type.
