Client: Reset frame callback timer when hiding a window

If we hide a window whilst a compositor has a pending frame to show,
it's possible the compositor will not render the frame and not return
the callback.

If this happens on the next window expose we can be left with
mFrameCallbackTimedOut still true causing isExposed() to remain false
and us to not send the next buffer when we later show the window again.

Change-Id: I507410415d1a930fd5fa736412055e68fdf6c1d3
Reviewed-by: Johan Helsing <johan.helsing@qt.io>

src/plugins/platforms/wayland/qwaylandwindow.cpp

@@ -254,6 +254,13 @@ void QWaylandWindow::reset(bool sendDestroyEvent)
         mFrameCallback = nullptr;
     }
 
+    int timerId  = mFrameCallbackTimerId.fetchAndStoreOrdered(-1);
+    if (timerId != -1) {
+        killTimer(timerId);
+    }
+    mWaitingForFrameCallback = false;
+    mFrameCallbackTimedOut = false;
+
     mMask = QRegion();
     mQueuedBuffer = nullptr;
 }