Fixed issue with level warp function depending on framerate

Whoops.

I think the problem was, although the value being added to the warp bar was multiplied by delta, the bar itself was then rounding the result to an integer. This meant if the amount to be added in a frame was below 0.5 it would be rounded to 0 and the bar wouldn't move.

So the warp progress was uncoupled from framerate and then coupled back to framerate but worse.  Good to know that can happen!

Thanks to RKJokela for making me aware of this.

Sorry if anyone else had this bug.  It's hopefully fixed now. :)