Merge pull request #21 from zacharied/fix.cli-dpi

Fix crash when converting chart with SvgString on CLI

OngekiFumenEditor/Base/EditorObjects/Svg/SvgStringPrefab.cs

@@ -84,7 +84,7 @@ public void RebuildSvgContent()
 			brush.Freeze();
 			var pen = new Pen(brush, 1);
 			pen.Freeze();
-			var dpiInfo = VisualTreeHelper.GetDpi(Application.Current.MainWindow);
+			var dpiInfo = Application.Current.MainWindow is not null ? VisualTreeHelper.GetDpi(Application.Current.MainWindow) : new();
 
 			var direction = ContentFlowDirection switch
 			{