segfault on KDE Plasma wayland

[Mamoru TASAKA]

Downstream bug: https://bugzilla.redhat.com/show_bug.cgi?id=2000812

On Fedora 34 KDE Plasma wayland session, using cairo-dock https://github.com/Cairo-Dock/cairo-dock-core/commit/6c569e67a2a366e7634224a0133ede51755629cb ,

`$ cairo-dock -c`

causes segfault at starup as atatched. This does not occur with GNOME + wayland - so apparently this is related to wayland implementation on KDE plasma.

So what is happening here is that cairo-dock calls wl_output_add_listener(), expecting that "geometry" information is to be returned first before "mode" information is gained. GNOME + wayland returns the information in this order, but KDE plasma + wayland returns in the opposite order.

Currently I don't know this behavior is allowed or not. But perhaps cairo-dock side can workaround this issue by allocating g_desktopGeometry.pScreens on _output_mode_cb() when the pointer is still NULL, perhaps? (at least this workaround seems to work for me).

You can try Fedora 34 KDE Plasma session from https://spins.fedoraproject.org/kde/download/index.html

[Mamoru TASAKA (mtasaka)]

So the legitimate way to fix this is to check "id" member of global registry object associated with that wl_output info.

Created: https://github.com/Cairo-Dock/cairo-dock-core/pull/12