Fix 'InvalidOperationException: Sequence contains no elements' in CaretReferenceHighlightRenderer.Draw

src/AddIns/BackendBindings/CSharpBinding/Project/Src/CaretReferenceHighlightRenderer.cs

@@ -79,6 +79,8 @@ namespace CSharpBinding
 		public void Draw(TextView textView, DrawingContext drawingContext)
 		{
 			if (currentReferences == null) {
+				if (textView.VisualLines.Count == 0)
+					return;
 				var start = textView.VisualLines.First().FirstDocumentLine.LineNumber;
 				var end = textView.VisualLines.Last().LastDocumentLine.LineNumber;
 				currentReferences = new List<ISegment>();