gtkapplication.c: Fix syntax error

Previous commit accidentally removed the closing } from
gtk_application_end_session(). Add it back to unbreak the build.

gtk/gtkapplication.c

@@ -1444,6 +1444,7 @@ gtk_application_end_session (GtkApplication         *application,
                          NULL, NULL, NULL);
       break;
     }
+}
 
 #else