Swiping/draging graph bug

[Neža Đukić]

I think there's a bug in the library. If you set panEdgeFraction to almost zero and then try to swipe a graph that is shorter than its dateWindow it jumps to the end and then refuse to move anymore.. + panEdgeFraction doesn't seem to work: when set to zero it pans to infinity and when set to something like 0.0000000001 you can still swipe something like 3% of the graph outside the broders..