Refactored getFirstLastIndex
Refactored getFirstLastIndex

Refactored the search for the first and last non-nil-entry into a
separate method (getFirstLastIndex)

leoMehlig/ios-charts,leoMehlig/Charts,leoMehlig/ios-charts,leoMehlig/Charts,leoMehlig/ios-charts,leoMehlig/ios-charts,leoMehlig/Charts,leoMehlig/Charts