[autotests] Update virtual desktop layout after load

Summary: This matches the behaviour of workspace.cpp on initial load.

Test Plan: Test now passes

Reviewers: #kwin, zzag

Reviewed By: #kwin, zzag

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D18183

autotests/test_screen_edges.cpp

@@ -298,6 +298,7 @@ void TestScreenEdges::testCreatingInitialEdges()
     auto vd = VirtualDesktopManager::self();
     vd->setConfig(config);
     vd->load();
+    vd->updateLayout();
     QCOMPARE(vd->count(), 4u);
     QCOMPARE(vd->grid().width(), 2);
     QCOMPARE(vd->grid().height(), 2);