Fixed bug in LineModulation.oPointsDummyFunc

[robqduquette]

Fixed a bug where oPointsDummyFunc would pick the wrong points and end up extrapolating from them instead of picking the right points and interpolating.

Eg, when interpolation should happen between x1 and x2, it would instead extrapolate between x2 and x3.
In the diagram below, when trying to interpolate at input Z(x), we would end up with Z*(x)

 Z
 ^             Z*
 |              \
 |      x1---Z--x2
 |                \
 |                 \
 |                  x3
 |
 +------------------------------> x

For another example, here is a desired modulation on a BaseCylinder for a pulley:

List<Vector3> aPoints = new List<Vector3>(){
    new Vector3(0f,     0f, fRad),
    new Vector3(fTransition,  0f, fRad),
    new Vector3(0.5f,   0f, fRadIn),
    new Vector3(1f - fTransition,  0f, fRad),
    new Vector3(1f,     0f, fRad)
};
LineModulation oPulleyShape = new LineModulation(aPoints, LineModulation.ECoord.Z, LineModulation.ECoord.X);

Previously this would result in an object like this:

Now this results in the intended shape: