slideshow: fix mysterious crash with the gtk3 vclplug

For some reason with gtk3 events are handled a bit differently, and in
particular after the PresenterSlideShowView::Resize() sets the
mbIsForcedPaintPending = true, with gtk2 we get a
notifySlideAnimationsEnded event and then a notifyViewChanged event that
calls PresenterSlideShowView::clear() to reset the flag,
but with gtk3 the flag isn't reset and then
PresenterSlideShowView::ForceRepaint() destroys the SlideView,
while there are still events in the EventQueue with pointers to it.

Since i'm evidently too dumb to tell what of this event handling is
working correctly and what is buggy, avoid the crash by checking
that the SlideView is still alive in the event handlers.

Change-Id: Ib88e61536c21e9787cef8a436341bfbd89914f4b

slideshow/source/engine/slideview.cxx

@@ -1038,6 +1038,30 @@ void SlideView::disposing( lang::EventObject const& evt )
     dispose();
 }
 
+// silly wrapper to check that event handlers don't touch dead SlideView
+struct WeakRefWrapper
+{
+    SlideView & m_rObj;
+    uno::WeakReference<uno::XInterface> const m_wObj;
+    std::function<void (SlideView&)> const m_func;
+
+    WeakRefWrapper(SlideView & rObj, std::function<void (SlideView&)> const& func)
+        : m_rObj(rObj)
+        , m_wObj(static_cast<::cppu::OWeakObject*>(&rObj))
+        , m_func(func)
+    {
+    }
+
+    void operator()()
+    {
+        uno::Reference<uno::XInterface> const xObj(m_wObj);
+        if (xObj.is())
+        {
+            m_func(m_rObj);
+        }
+    }
+};
+
 // XModifyListener
 void SlideView::modified( const lang::EventObject& /*aEvent*/ )
     throw (uno::RuntimeException, std::exception)
@@ -1081,7 +1105,8 @@ void SlideView::modified( const lang::EventObject& /*aEvent*/ )
     // notify view change. Don't call EventMultiplexer directly, this
     // might not be the main thread!
     mrEventQueue.addEvent(
-        makeEvent( [this] () { this->mrEventMultiplexer.notifyViewChanged(this->mxView); },
+        makeEvent( WeakRefWrapper(*this,
+            [] (SlideView & rThis) { rThis.mrEventMultiplexer.notifyViewChanged(rThis.mxView); }),
                    "EventMultiplexer::notifyViewChanged"));
 }
 
@@ -1096,7 +1121,8 @@ void SlideView::windowPaint( const awt::PaintEvent& /*e*/ )
     // notify view clobbering. Don't call EventMultiplexer directly,
     // this might not be the main thread!
     mrEventQueue.addEvent(
-        makeEvent( [this] () { this->mrEventMultiplexer.notifyViewClobbered(this->mxView); },
+        makeEvent( WeakRefWrapper(*this,
+            [] (SlideView & rThis) { rThis.mrEventMultiplexer.notifyViewClobbered(rThis.mxView); }),
                    "EventMultiplexer::notifyViewClobbered") );
 }