make quick switch gesture properly open switcher on end of list

doing a quick task switch gesture towards the end of the list should force open the task switcher (there is nothing to switch to).

this was half-done on the left side of the switcher (this behavior is not visible with immediate task reordering, but could be hit if we have different ordering criteria or delayed reordering), but had remaining syntax from the old behavior that was only syntactically correct by accident (wtf JS?).

due to superfluous Math.max this was completely not working on the right side, ending up in always opening the right-most task instead of opening the switcher