yet another overrun access of an empty OUString

no impact in release build but triiger assert in debug

Change-Id: I037cf127ff55c03dbc5e151d1373cfb4f6219848
fdo#69162 avoid crashing on Accellerator in poorly initialized context

Change-Id: If3446ae33f2c2e737acf56bb523519e7b9d9935e