Prevent null ptr exception caused by clicking on variable color of empty line after deleting the existing variable name on the list in Geometry and Plot Watch.

Author: awulkiew

Visual_Studio_2017/GraphicalDebugging/GeometryWatchControl.xaml.cs

@@ -546,7 +546,7 @@ private void colorTextBlock_MouseDown(object sender, System.Windows.Input.MouseB
         {
             TextBlock textBlock = sender as TextBlock;
             GeometryItem geometry = textBlock.DataContext as GeometryItem;
-            if (geometry.ColorId >= 0)
+            if (geometry != null && geometry.ColorId >= 0)
             {
                 var color = (textBlock.Background as System.Windows.Media.SolidColorBrush).Color;
                 var newColor = Util.ShowColorDialog(color);

Visual_Studio_2017/GraphicalDebugging/PlotWatchControl.xaml.cs

@@ -553,7 +553,7 @@ private void colorTextBlock_MouseDown(object sender, System.Windows.Input.MouseB
         {
             TextBlock textBlock = sender as TextBlock;
             PlotItem geometry = textBlock.DataContext as PlotItem;
-            if (geometry.ColorId >= 0)
+            if (geometry != null && geometry.ColorId >= 0)
             {
                 var color = (textBlock.Background as System.Windows.Media.SolidColorBrush).Color;
                 var newColor = Util.ShowColorDialog(color);