Show warning when local clone already exists

"You have already cloned to this location. Click 'Open' to open the
local repository."

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

@@ -267,6 +267,8 @@ namespace GitHub.ViewModels.Dialog.Clone
                         {
                             return string.Format(CultureInfo.CurrentCulture, Resources.LocalRepositoryHasARemoteOf, localUrl);
                         }
+
+                        return Resources.YouHaveAlreadyClonedToThisLocation;
                     }
                 }
             }

src/GitHub.Resources/Resources.Designer.cs

@@ -2180,6 +2180,15 @@ namespace GitHub {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to You have already cloned to this location. Click &apos;Open&apos; to open the local repository..
+        /// </summary>
+        public static string YouHaveAlreadyClonedToThisLocation {
+            get {
+                return ResourceManager.GetString("YouHaveAlreadyClonedToThisLocation", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to You must commit and push your changes to add a comment here..
         /// </summary>

src/GitHub.Resources/Resources.resx

@@ -833,4 +833,7 @@ https://git-scm.com/download/win</value>
   <data name="LocalRepositoryHasARemoteOf" xml:space="preserve">
     <value>Local repository has a remote of {0}.</value>
   </data>
+  <data name="YouHaveAlreadyClonedToThisLocation" xml:space="preserve">
+    <value>You have already cloned to this location. Click 'Open' to open the local repository.</value>
+  </data>
 </root>