Consolidate PathError into PathWarning

There was an issue with PathError appearing at the top. When the error
appeared, the repository list would move down causing a different
repository to be selected. This would clause flickering between two
repositories.

This commit consolidates PathError into PathWarning (which appears
above the path which is being validated).  This avoids the flicker and
puts the warning next to the text box which it applies to.

The logic to block clone or open when there is a file in the way has
been moved to the commands' `canExecute` observable.

Author: jcansdale

src/GitHub.App/SampleData/Dialog/Clone/RepositoryCloneViewModelDesigner.cs

@@ -16,7 +16,6 @@ public RepositoryCloneViewModelDesigner()
         }
 
         public string Path { get; set; }
-        public string PathError { get; set; }
         public string PathWarning { get; set; }
         public int SelectedTabIndex { get; set; }
         public string Title => null;

src/GitHub.App/ViewModels/Dialog/Clone/RepositoryCloneViewModel.cs

@@ -29,7 +29,6 @@ public class RepositoryCloneViewModel : ViewModelBase, IRepositoryCloneViewModel
         readonly IReadOnlyList<IRepositoryCloneTabViewModel> tabs;
         string path;
         IRepositoryModel previousRepository;
-        ObservableAsPropertyHelper<string> pathError;
         ObservableAsPropertyHelper<string> pathWarning;
         int selectedTabIndex;
 
@@ -63,25 +62,19 @@ public RepositoryCloneViewModel(
             Path = service.DefaultClonePath;
             repository.Subscribe(x => UpdatePath(x));
 
-            pathError = Observable.CombineLatest(
-                repository,
-                this.WhenAnyValue(x => x.Path),
-                ValidatePathError)
-                .ToProperty(this, x => x.PathError);
-
             pathWarning = Observable.CombineLatest(
                 repository,
                 this.WhenAnyValue(x => x.Path),
                 ValidatePathWarning)
                 .ToProperty(this, x => x.PathWarning);
 
             var canClone = Observable.CombineLatest(
-                repository, this.WhenAnyValue(x => x.Path), this.WhenAnyValue(x => x.PathError),
-                (repo, path, error) => repo != null && error == null && !service.DestinationDirectoryExists(path));
+                repository, this.WhenAnyValue(x => x.Path),
+                (repo, path) => repo != null && !service.DestinationFileExists(path) && !service.DestinationDirectoryExists(path));
 
             var canOpen = Observable.CombineLatest(
-                repository, this.WhenAnyValue(x => x.Path), this.WhenAnyValue(x => x.PathError),
-                (repo, path, error) => repo != null && error == null && service.DestinationDirectoryExists(path));
+                repository, this.WhenAnyValue(x => x.Path),
+                (repo, path) => repo != null && !service.DestinationFileExists(path) && service.DestinationDirectoryExists(path));
 
             Browse = ReactiveCommand.Create().OnExecuteCompleted(_ => BrowseForDirectory());
             Clone = ReactiveCommand.CreateAsyncObservable(
@@ -102,8 +95,6 @@ public string Path
             set => this.RaiseAndSetIfChanged(ref path, value);
         }
 
-        public string PathError => pathError.Value;
-
         public string PathWarning => pathWarning.Value;
 
         public int SelectedTabIndex
@@ -247,22 +238,15 @@ string FindDirWithout(string dir, string match, int levels)
             }
         }
 
-        string ValidatePathError(IRepositoryModel repository, string path)
-        {
-            if (repository != null)
-            {
-                return service.DestinationFileExists(path) ?
-                    Resources.DestinationAlreadyExists :
-                    null;
-            }
-
-            return null;
-        }
-
         string ValidatePathWarning(IRepositoryModel repositoryModel, string path)
         {
             if (repositoryModel != null)
             {
+                if (service.DestinationFileExists(path))
+                {
+                    return Resources.DestinationAlreadyExists;
+                }
+
                 if (service.DestinationDirectoryExists(path))
                 {
                     using (var repository = gitService.GetRepository(path))

src/GitHub.Exports.Reactive/ViewModels/Dialog/Clone/IRepositoryCloneViewModel.cs

@@ -5,7 +5,7 @@
 namespace GitHub.ViewModels.Dialog.Clone
 {
     /// <summary>
-    /// ViewModel for the the Clone Repository dialog
+    /// ViewModel for the Clone Repository dialog
     /// </summary>
     public interface IRepositoryCloneViewModel : IDialogContentViewModel, IConnectionInitializedViewModel
     {
@@ -29,11 +29,6 @@ public interface IRepositoryCloneViewModel : IDialogContentViewModel, IConnectio
         /// </summary>
         string Path { get; set; }
 
-        /// <summary>
-        /// Gets an error message that explains why <see cref="Path"/> is not valid.
-        /// </summary>
-        string PathError { get; }
-
         /// <summary>
         /// Gets a warning message that explains why <see cref="Path"/> is suspect.
         /// </summary>

src/GitHub.VisualStudio/Views/Dialog/Clone/RepositoryCloneView.xaml

@@ -21,8 +21,6 @@
     </UserControl.Resources>
 
     <DockPanel>
-        <ghfvs:InfoPanel Message="{Binding PathError}"/>
-
         <StackPanel Orientation="Horizontal" DockPanel.Dock="Bottom" HorizontalAlignment="Center">
             <ghfvs:OcticonCircleButton
                                    Margin="12"