KWayland::Client::Surface track output destruction

Summary:
A compositor should send left events before deleting an output; however
if it doesn't, we don't want dangly pointers in our list of outputs on
the client surface.

Test Plan: Unit test

Reviewers: #plasma, graesslin

Reviewed By: #plasma, graesslin

Subscribers: plasma-devel, #frameworks

Tags: #plasma_on_wayland, #frameworks

Differential Revision: https://phabricator.kde.org/D7379

src/wayland/autotests/client/test_wayland_surface.cpp

@@ -1076,6 +1076,12 @@ void TestWaylandSurface::testOutput()
     QVERIFY(enteredSpy.wait());
     QCOMPARE(enteredSpy.count(), 2);
     QCOMPARE(leftSpy.count(), 1);
+
+    //test the client handles a misbehaving server that removes a display before updating clients
+    m_display->removeOutput(serverOutput);
+    QCOMPARE(leftSpy.count(), 1);
+    QVERIFY(s->outputs().isEmpty());
+
 }
 
 QTEST_GUILESS_MAIN(TestWaylandSurface)