Check if we successfully restored input focus

In rare cases, Workspace::restoreFocus() may fail, for example when the
most recently activated client is about to be destroyed or unmapped.

If it happens that we cannot restore the focus, then mark the window in
FocusIn event as active.

CCBUG: 424223

(cherry picked from commit 55588507)
(cherry picked from commit 892d2ad1)