panelMenu: Only try to navigate in menu when an item is selected

Only allow navigating outside the menu (to switch to another menu or to
close the current menu) if the menu didn't handle the event itself or if
the menu actor is still focused (we focus the menu actor by default
after opening a menu).

GNOME/gnome-shell!277
6 jobs for !277 with popup-menu-keyboard-nav in 8 minutes and 38 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Review
passed #370578
check_commit_log

00:00:22

passed #370580
eslint

00:01:07

passed #370579
js_check

00:00:39

 
  Build
passed #370581
build

00:05:56

 
  Test
passed #370582
test

00:01:35

passed #370583
test-pot

00:01:34