When opening undo stack, always start at the top

[wayfaringrob]

I noticed (the hard way) that if you expand the undo menu, it doesn't necessarily start at the top (see scrollbar). Rather, it remembers your last location.

That means that one could easily click it, click the first or second entry, and accidentally undo several more steps than anticipated. It would help as a guardrail if the list always snapped to the top when opening.