vtkChartBox: initialize segmentIndex

It isn't used in the called function and it seems that -1 is the
"invalid" value for it (based on vtkPlotBarPrivate::GetNearestPoint as
called from vtkChartXY::LocatePointInPlot).

Change-Id: Ib89ba0490345bed56d7502b209fcb962a02e28de
nit: remove extra semicolon

Change-Id: I4085ec6d324d7260543c0ff90c4a221314ee7f0a
Merge topic 'dashboard-warnings-20130716' into master

a09107ca nit: remove extra semicolon
eda45be1 vtkChartBox: initialize segmentIndex