[wayland] avoid potential crash when checking for window inhibitions on desktop change

Summary:
Xwayland clients are sometimes offset from being visible to having a
surface applied.

We might also have internal windows which will be AbstractClients
without a surface.

No idle interface will be set up for non wayland clients, but on a
desktop change we itterate through all AbstractClients and need to guard
somewhere.

BUG: 420039

Test Plan: None

Reviewers: #kwin, apol

Reviewed By: apol

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D28858

idle_inhibition.cpp

@@ -101,7 +101,7 @@ void IdleInhibition::update(AbstractClient *client)
     // TODO: Don't honor the idle inhibitor object if the shell client is not
     // on the current activity (currently, activities are not supported).
     const bool visible = client->isShown(true) && client->isOnCurrentDesktop();
-    if (visible && client->surface()->inhibitsIdle()) {
+    if (visible && client->surface() && client->surface()->inhibitsIdle()) {
         inhibit(client);
     } else {
         uninhibit(client);