chart::ChartController::queryGL3DChart(): crash on concurrent model close

As seen in JunitTest_chart2_unoapi
[sch.ChXChartDocument::com::sun::star::beans::XPropertySet]
it is possible that one thread closes the model while the main thread
tries to paint the chart via timeout.
In  chart::ChartController::modeChanged() It's not obviously possible
to lock m_aModelMutex since that might deadlock with SolarMutex.

6  in SolarMutexGuard::SolarMutexGuard (this=0x2b742f846cc0) at /include/vcl/svapp.hxx:1579
7  in (anonymous namespace)::Frame::isActionLocked (this=0x1dbe1b0) at /framework/source/services/frame.cxx:2597
8  in (anonymous namespace)::Frame::close (this=0x1dbe1b0, bDeliverOwnership=0 '\000') at /framework/source/services/frame.cxx:1773
9  in chart::ChartController::notifyClosing (this=0x1e4ec00, rSource=...) at /chart2/source/controller/main/ChartController.cxx:877
10 in apphelper::CloseableLifeTimeManager::impl_doClose (this=0x1e03b98) at /chart2/source/tools/LifeTime.cxx:368
11 in apphelper::CloseableLifeTimeManager::g_close_endTryClose_doClose (this=0x1e03b98) at /chart2/source/tools/LifeTime.cxx:311
12 in chart::ChartModel::close (this=0x1e03ac0, bDeliverOwnership=1 '\001') at /chart2/source/model/main/ChartModel.cxx:654

main thread:

21 in chart::ChartController::TheModel::getModel (this=0x0) at /chart2/source/controller/main/ChartController.hxx:470
22 in chart::ChartController::queryGL3DChart (this=0x1e4ec00) at /chart2/source/controller/main/ChartController.cxx:1398
23 in chart::ChartController::modeChanged (this=0x1e4ec00, rEvent=...) at /chart2/source/controller/main/ChartController.cxx:486
24 in chart::ChartView::impl_notifyModeChangeListener (this=0x1e149f0, rNewMode="valid") at /chart2/source/view/main/ChartView.cxx:2823
25 in chart::ChartView::impl_updateView (this=0x1e149f0) at /chart2/source/view/main/ChartView.cxx:2730
26 in chart::ChartView::update (this=0x1e149f0) at /chart2/source/view/main/ChartView.cxx:2861
27 in chart::ChartController::execute_Paint (this=0x1e4ec00, rRect=Rectangle = {...}) at /chart2/source/controller/main/ChartController_Window.cxx:493
28 in chart::ChartWindow::Paint (this=0x201c970, rRect=Rectangle = {...}) at /chart2/source/controller/main/ChartWindow.cxx:83

Change-Id: Ib99edbb9862bc9dab76ed3e0c21eca5589fe7fdb

chart2/source/controller/main/ChartController.cxx

@@ -1395,9 +1395,13 @@ void ChartController::queryGL3DChart()
 {
     m_bGL3DChart = false;
 
-    uno::Reference<frame::XModel> xModel = m_aModel->getModel();
-    if (!xModel.is())
+    uno::Reference<frame::XModel> xModel;
+    {   // it's possible that model was cleared by a different thread!
+        osl::MutexGuard g(m_aModelMutex);
+        if (!m_aModel.is())
             return;
+        xModel = m_aModel->getModel();
+    }
 
     uno::Reference<XChartDocument> xChartDoc(xModel, uno::UNO_QUERY);
     if (!xChartDoc.is())