Fix: 'Reset Curve' applies incorrect transformation for positive slopes

Currently, the 'Reset Curve' button, corresponding to the
`BKE_curvemap_reset` function, converts a predefined negative slope
curve to a positive slope by inverting the order of y axis points. This
has the implicit dependency on these points being at inverse x
positions. For most preset curves, this works well, but for the round
curve, which has points at 0, 0.5, 0.86, and 1, this condition does not
hold true.

To fix this, take the inverted x value for a given control point
instead of the raw value. For the above example this means that the
round curve now has x values at 0, 0.14, 0.5, and 1.

Pull Request: https://projects.blender.org/blender/blender/pulls/147008

source/blender/blenkernel/intern/colortools.cc

@@ -433,6 +433,7 @@ void BKE_curvemap_reset(CurveMap *cuma, const rctf *clipr, int preset, CurveMapS
     CurveMapPoint *newpoints = static_cast<CurveMapPoint *>(MEM_dupallocN(cuma->curve));
 
     for (i = 0; i < cuma->totpoint; i++) {
+      newpoints[i].x = 1.0f - cuma->curve[last - i].x;
       newpoints[i].y = cuma->curve[last - i].y;
     }