Fix #3402: System.NullReferenceException on right click on .NET 9 (#3403)

* Fix #3402: System.NullReferenceException on right click on .NET 9

* Add comments to clarify about used design pattern

Directory.Packages.props

@@ -45,10 +45,10 @@
     <PackageVersion Include="System.Reflection.Metadata" Version="9.0.1" />
     <PackageVersion Include="System.Resources.Extensions" Version="9.0.1" />
     <PackageVersion Include="System.Runtime.CompilerServices.Unsafe" Version="6.1.0" />
-    <PackageVersion Include="TomsToolbox.Composition.MicrosoftExtensions" Version="2.21.0" />
-    <PackageVersion Include="TomsToolbox.Wpf.Composition" Version="2.20.0" />
-    <PackageVersion Include="TomsToolbox.Wpf.Composition.AttributedModel" Version="2.21.0" />
-    <PackageVersion Include="TomsToolbox.Wpf.Styles" Version="2.21.0" />
+    <PackageVersion Include="TomsToolbox.Composition.MicrosoftExtensions" Version="2.22.0" />
+    <PackageVersion Include="TomsToolbox.Wpf.Composition" Version="2.22.0" />
+    <PackageVersion Include="TomsToolbox.Wpf.Composition.AttributedModel" Version="2.22.0" />
+    <PackageVersion Include="TomsToolbox.Wpf.Styles" Version="2.22.0" />
     <PackageVersion Include="coverlet.collector" Version="6.0.3" />
     <PackageVersion Include="System.Net.Http" Version="4.3.4" />
     <PackageVersion Include="System.Private.Uri" Version="4.3.2" />

ILSpy/AssemblyTree/AssemblyTreeModel.cs

@@ -767,6 +767,8 @@ namespace ICSharpCode.ILSpy.AssemblyTree
 				}
 				else
 				{
+					// ensure that we are only connected once to the event, else we might get multiple notifications
+					ContextMenuProvider.ContextMenuClosed -= ContextMenuClosed;
 					ContextMenuProvider.ContextMenuClosed += ContextMenuClosed;
 				}
 			}