Make ratelimitedfunc time from the function's end
Otherwise any function tghat takes longer than the delay to execute
will become eligible for execution again immediately after
finishing and therefore be able to spin.
This should help with https://github.com/vector-im/riot-web/issues/6060
(at least in the respect that it makes ratelimitedfunc do its job)
even if it's not the reason Riot started getting wedged.
