Fix off-by-one error in ComputeBounds() for vtkPlotPoints

This fixes an off-by-one error in ComputeBounds() for vtkPlotPoints
when the input data has bad points (NaN's/Inf's). The bad points
index variable (i) was being incremented before looking up the next
bad point causing the range to be too large. In that case a NaN value
could be used in the calculation causing the function to return
(NaN - NaN) as the bounds for the data.

This fixes the pv.SLACTools test in ParaView.

Change-Id: I12c1768d87c6f07af979333b70d8abb4ae2d2796
Merge topic 'fix-plot-points-bounds-bug' into master

6f7d3a61 Fix off-by-one error in ComputeBounds() for vtkPlotPoints