Merge pull request #603 from tig/application_shutdown_crash

Fixes UI Catalog shutdown crash

Terminal.Gui/Core/Application.cs

@@ -480,7 +480,7 @@ namespace Terminal.Gui {
 			// Closes the application if it's true.
 			if (closeDriver) {
 				MainLoop = null;
-				Driver.End ();
+				Driver?.End ();
 				Driver = null;
 			}
 

UICatalog/UICatalog.cs

@@ -88,8 +88,6 @@ namespace UICatalog {
 				scenario.Run ();
 				scenario = GetScenarioToRun ();
 			}
-			// Now closes the driver too.
-			Application.Shutdown ();
 		}
 
 		/// <summary>