Fixed bugs in the map vote plugin.

- RTV votes that extended the map would overwrite the current cycle time
left and leave only the extension time left, rather than extending the
cycle time.
- RTV votes that finished early would not remove the vote option from
the vote menu until their full time was up.
- Next map votes taken part way through a map would also replace the
remaining cycle time with the extension time, they now extend the
remaining cycle time properly.