ComPDFKit.Demo(win) - 修复创建测量注释时，点到其他测量注释崩溃的问题

Demo/Examples/Compdfkit.Controls/Measure/MeasureControl.xaml.cs

@@ -282,10 +282,11 @@ namespace ComPDFKit.Controls.Measure
 
         private void SetMeasureInfoPanel(CPDFAnnotation annot,AnnotParam param = null)
         {
-            if (annot == null)
+            if (annot == null || !annot.IsValid())
             {
                 return;
             }
+
             try
             {
                 if (annot.Type == C_ANNOTATION_TYPE.C_ANNOTATION_LINE)