fix: document not appears when loaded

Author: HelloWRC

Markdown.Avalonia.Tight/MarkdownScrollViewer.cs

@@ -21,6 +21,7 @@
 using System.Linq;
 using System.Net.Http;
 using System.Text.RegularExpressions;
+using Avalonia.LogicalTree;
 using MdStyle = Markdown.Avalonia.MarkdownStyle;
 
 namespace Markdown.Avalonia
@@ -148,6 +149,13 @@ public MarkdownScrollViewer()
             _viewer.Content = _wrapper;
         }
 
+        protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
+        {
+            base.OnAttachedToVisualTree(e);
+            
+            UpdateMarkdown();
+        }
+
         #region text selection
 
         private bool _isLeftButtonPressed;