Update JpGraphRendererBase.php - check existing of PlotLabel

I've got
Uncaught PHP Exception Symfony\Component\ErrorHandler\Error\FatalError: "Error: Uncaught Error: Call to a member function getDataValue() on bool in .../vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Chart/Renderer/JpGraphRendererBase.php:337

I found that it's necessary to check existing of PlotLabel before using its method getDataValue().

Author: yfinkel

src/PhpSpreadsheet/Chart/Renderer/JpGraphRendererBase.php

@@ -334,7 +334,8 @@ private function renderPlotLine(int $groupID, bool $filled = false, bool $combin
                 //    Set the appropriate plot marker
                 $this->formatPointMarker($seriesPlot, $marker);
             }
-            $dataLabel = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotLabelByIndex($index)->getDataValue();
+            if ($this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotLabelByIndex($index))
+                $dataLabel = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotLabelByIndex($index)->getDataValue();
             $seriesPlot->SetLegend($dataLabel);
 
             $seriesPlots[] = $seriesPlot;