Other "if able" abilities, like Hourglass' subroutines, drain clicks one at a time. False Lead, on the other hand, lumps two clicks into one ability. IIRC, Tollbooth's conditional ability does not drain credits if the runner has insufficient funds.

If the runner only has one click remaining, does activating False Lead's ability drain it away?

I would say No, it either removes 2 clicks or none. It should function just like Tollbooth's abilitly.

If it were to aways be able to remove clicks it would say "The runner loses 'click' if able, and then the runner loses 'click' if able."