849 prep fill area cleanup

@doutriaux1 @aashish24 

Had an hour to kill and took a stab at optimizing the vcs scalar bar implementation. Ended up cutting the time down from 0.262s to 0.89s on my machine.

Ref #849 
@dlonie I think what the code was trying to before was filling the list to make their length match. Using the last elements. I think your change would break things like:
fa.x = [.25,.75]
fa.y = [1,]

But you are probably right it is probably better to simply error exit in such cases.