Bug in dispose member fix

[JohanLarsson]

    public sealed partial class MainWindow : Window, IDisposable
    {
        private readonly ServiceHost _serviceHost;
        private bool _disposed;

        public MainWindow()
        {
            InitializeComponent();
            var service = new TapWcfService(vm);
            _serviceHost = new ServiceHost(service);
            _serviceHost.Open();
        }

        public void Dispose()
        {
            if (_disposed)
            {
                return;
            }

            _disposed = true;
        }
    }

System.InvalidOperationException : Should never get here.
   at Gu.Roslyn.AnalyzerExtensions.FieldOrProperty.Initializer(CancellationToken cancellationToken)
   at IDisposableAnalyzers.IDisposableFactory.MemberAccessContext.Create(FieldOrProperty disposable,MethodDeclarationSyntax method,SemanticModel semanticModel,CancellationToken cancellationToken)
   at IDisposableAnalyzers.IDisposableFactory.DisposeStatement(FieldOrProperty disposable,MethodDeclarationSyntax method,SemanticModel semanticModel,CancellationToken cancellationToken)
   at IDisposableAnalyzers.DisposeMemberFix.<>c__DisplayClass3_5.<RegisterCodeFixesAsync>b__12(BlockSyntax x)
   at Gu.Roslyn.CodeFixExtensions.DocumentEditorExt.<>c__DisplayClass11_0`1.<ReplaceNode>b__0(SyntaxNode x,SyntaxGenerator _)
   at Microsoft.CodeAnalysis.Editing.SyntaxEditor.ReplaceChange.Apply(SyntaxNode root,SyntaxGenerator generator)
   at Microsoft.CodeAnalysis.Editing.SyntaxEditor.GetChangedRoot()
   at async Gu.Roslyn.CodeFixExtensions.DocumentEditorAction.GetChangedDocumentAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.GetChangedSolutionAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.ComputeOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.GetPreviewOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Editor.Implementation.Suggestions.SuggestedAction.GetPreviewResultAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Editor.Implementation.Suggestions.SuggestedActionWithNestedFlavors.<>c__DisplayClass11_0.<GetPreviewAsync>b__0(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Extensions.IExtensionManagerExtensions.PerformFunctionAsync[T](<Unknown Parameters>)