bugfix to BaseSingleSessionApp with empty session after trying to open the session that was already open

Author: rjackey

widgets/+wt/+apps/BaseSingleSessionApp.m

@@ -124,9 +124,11 @@ function close(app)
             % Call superclass internal load method
             session = app.loadSession_Internal(sessionPath);
 
-            % Store the session
+            % If successful, store the session
             % This also triggers app.update(), app.updateTitle()
-            app.Session = session;
+            if isscalar(session) && isvalid(session)
+                app.Session = session;
+            end
 
         end %function