io/router: don't panic on focus moves when there is nothing to focus

Signed-off-by: Elias Naur <mail@eliasnaur.com>

io/router/key.go

@@ -171,6 +171,9 @@ func (q *keyQueue) updateFocusLayout() {
 
 // MoveFocus attempts to move the focus in the direction of dir, returning true if it succeeds.
 func (q *keyQueue) MoveFocus(dir FocusDirection, events *handlerEvents) bool {
+	if len(q.dirOrder) == 0 {
+		return false
+	}
 	order := 0
 	if q.focus != nil {
 		order = q.handlers[q.focus].dirOrder

io/router/key_test.go

@@ -311,6 +311,11 @@ func TestFocusClick(t *testing.T) {
 	assertEventPointerTypeSequence(t, r.Events(h), pointer.Cancel, pointer.Press, pointer.Release)
 }
 
+func TestNoFocus(t *testing.T) {
+	r := new(Router)
+	r.MoveFocus(FocusForward)
+}
+
 func assertKeyEvent(t *testing.T, events []event.Event, expected bool, expectedInputs ...event.Event) {
 	t.Helper()
 	var evtFocus int