Fix LineSeries NullReferenceException (#499)

NullReferenceException in LineSeries.GetNearestPoints() when Smooth =
true

CHANGELOG.md

@@ -77,6 +77,7 @@ All notable changes to this project will be documented in this file.
 - Inaccurate tracker when using LogarithmicAxis (#443)
 - Fix reset of transforms in WinForms render context (#489)
 - Fix StringFormat for TimeSpanAxis not recognizing f, ff, fff, etc (#330)
+- Fix  LineSeries SMOOTH=True will crash WinForms on right click (#499)
 
 ## [2014.1.546] - 2014-10-22
 ### Added