tdf#42915, NaN in a date axis can destroy the whole chart

The NaN value forces the scaling of the axis to be based on years
and introduces gaps in the rendering.

Change-Id: I78219be289d76edb53b5672209e1c031ab62def9
Reviewed-on: https://gerrit.libreoffice.org/64267
Tested-by: Jenkins
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

chart2/source/view/charttypes/AreaChart.cxx

@@ -718,7 +718,12 @@ void AreaChart::createShapes()
                     //collect data point information (logic coordinates, style ):
                     double fLogicX = pSeries->getXValue(nIndex);
                     if (bDateCategory)
+                    {
+                        if (rtl::math::isNan(fLogicX))
+                            continue;
+
                         fLogicX = DateHelper::RasterizeDateValue( fLogicX, m_aNullDate, m_nTimeResolution );
+                    }
                     double fLogicY = pSeries->getYValue(nIndex);
 
                     if( m_nDimension==3 && m_bArea && rXSlot.m_aSeriesVector.size()!=1 )

chart2/source/view/charttypes/VSeriesPlotter.cxx

@@ -1451,10 +1451,17 @@ long VSeriesPlotter::calculateTimeResolutionOnXAxis()
         if( !rDateCategories.empty() )
         {
             std::vector< double >::const_iterator aIt = rDateCategories.begin(), aEnd = rDateCategories.end();
+            while (rtl::math::isNan(*aIt) && aIt != aEnd)
+            {
+                ++aIt;
+            }
             Date aPrevious(aNullDate); aPrevious.AddDays(rtl::math::approxFloor(*aIt));
             ++aIt;
             for(;aIt!=aEnd;++aIt)
             {
+                if (rtl::math::isNan(*aIt))
+                    continue;
+
                 Date aCurrent(aNullDate); aCurrent.AddDays(rtl::math::approxFloor(*aIt));
                 if( nRet == css::chart::TimeUnit::YEAR )
                 {