Add extra null guard

Author: ThomasKroes

src/ScalarAction.cpp

@@ -29,13 +29,16 @@ ScalarAction::ScalarAction(QObject* parent, const QString& title, const float& m
             if (auto scatterplotPlugin = dynamic_cast<ScatterplotPlugin*>(findPluginAncestor())) {
                 auto positionDataset            = scatterplotPlugin->getPositionDataset();
                 auto scalarSourcePointsDataset  = Dataset<Points>(getCurrentDataset());
-                const auto numScalars           = scalarSourcePointsDataset->getNumPoints();
-                const auto numPositions         = positionDataset->getNumPoints();
 
-                if (numScalars != numPositions) {
-                    emitSourceSelectionChanged = false;
+                if (scalarSourcePointsDataset.isValid() && positionDataset.isValid()) {
+	                const auto numScalars   = scalarSourcePointsDataset->getNumPoints();
+					const auto numPositions = positionDataset->getNumPoints();
 
-                    scatterplotPlugin->addNotification(QString("The number of points in the scalar source dataset does not match the number of points in the position dataset. (numPositions=%1, numScalars:%2)").arg(QString::number(numPositions), QString::number(numScalars)));
+					if (numScalars != numPositions) {
+						emitSourceSelectionChanged = false;
+
+						scatterplotPlugin->addNotification(QString("The number of points in the scalar source dataset does not match the number of points in the position dataset. (numPositions=%1, numScalars:%2)").arg(QString::number(numPositions), QString::number(numScalars)));
+					}
                 }
             }
         } else {