Fix: Base/derived types nodes in ClassBrowser not filled, because no lazy loading active.

src/Main/Base/Project/Dom/ClassBrowser/BaseTypesTreeNode.cs

@@ -40,17 +40,13 @@ namespace ICSharpCode.SharpDevelop.Dom.ClassBrowser
 				throw new ArgumentNullException("definition");
 			this.definition = definition;
 			this.text = SD.ResourceService.GetString("MainWindow.Windows.ClassBrowser.BaseTypes");
+			LazyLoading = true;
 		}
 		
 		protected override void OnIsVisibleChanged()
 		{
 			base.OnIsVisibleChanged();
-			if (IsVisible) {
 			definition.Updated += OnDefinitionUpdated;
-			} else {
-				definition.Updated -= OnDefinitionUpdated;
-				LazyLoading = true;
-			}
 		}
 		
 		void OnDefinitionUpdated(object sender, EventArgs e)

src/Main/Base/Project/Dom/ClassBrowser/DerivedTypesTreeNode.cs

@@ -38,17 +38,13 @@ namespace ICSharpCode.SharpDevelop.Dom.ClassBrowser
 				throw new ArgumentNullException("definition");
 			this.definition = definition;
 			this.text = SD.ResourceService.GetString("MainWindow.Windows.ClassBrowser.DerivedTypes");
+			LazyLoading = true;
 		}
 		
 		protected override void OnIsVisibleChanged()
 		{
 			base.OnIsVisibleChanged();
-			if (IsVisible) {
 			definition.Updated += OnDefinitionUpdated;
-			} else {
-				definition.Updated -= OnDefinitionUpdated;
-				LazyLoading = true;
-			}
 		}
 		
 		void OnDefinitionUpdated(object sender, EventArgs e)