The ulsPopup variable is local to the showUndoTooltip() function.
If it is called multiple times, then a previous assignment of an
OO.ui.PopupWidget object would not be found here in subsequent calls.
This check can only ever be false since it is the first statement in
the function (after variable and function declarations, which don't
do anything other than call `$()`).
Change-Id: I7020c103428d01b5e48c65be695471401f588fc4
a6e0c10c54