VTk Bug16140: Add one-point line&triangle check for vtkPolyData

VTK constructs VTK_LINE as two points. However, if reading file that defines it with only one point, it would define the line goes from (x,y,z) to (0,0,0) which would cause downstream problems(Ex. (0,0,0) would fall outside of the dataset bounds since it's not in the point dataset). So when calling vtkPolyData::BuildCell,condition checks are added to warn the user that they are reading one-point lines. So does the triangles.

One small concern is about the speed, but my understanding is that since numCellPts has already been tested before, so it would be stored in CPU L1 caches/registers, which causes a minimal impact.

Issue report #16140 (closed).