Only consider a containment as finished if it actually passes a "true".

So far, we were only considering the fact that teh signal was being
emitted, and that's doesn't seem correct.

REVIEW: 119191

src/plasma/corona.cpp

@@ -532,7 +532,10 @@ QList<Plasma::Containment *> CoronaPrivate::importLayout(const KConfigGroup &con
         foreach (Containment *containment, containments) {
             if (!containment->isUiReady() && containment->lastScreen() < q->numScreens()) {
                 ++containmentsStarting;
-                QObject::connect(containment, &Plasma::Containment::uiReadyChanged, [ = ]() {
+                QObject::connect(containment, &Plasma::Containment::uiReadyChanged, [=](bool ready) {
+                    if (!ready)
+                        return;
+
                     --containmentsStarting;
                     if (containmentsStarting <= 0) {
                         emit q->startupCompleted();