Curve Fitting: avoid clamping fallback handles.

extern/curve_fit_nd/intern/curve_fit_cubic.c

@@ -471,11 +471,16 @@ static void cubic_from_points(
 	 * so only problems absurd of approximation and not for bugs in the code.
 	 */
 
+	bool use_clamp = true;
+
 	/* flip check to catch nan values */
 	if (!(alpha_l >= 0.0) ||
 	    !(alpha_r >= 0.0))
 	{
 		alpha_l = alpha_r = len_vnvn(p0, p3, dims) / 3.0;
+
+		/* skip clamping when we're using default handles */
+		use_clamp = false;
 	}
 
 	double *p1 = CUBIC_PT(r_cubic, 1, dims);
@@ -497,6 +502,7 @@ static void cubic_from_points(
 	/* ------------------------------------
 	 * Clamping (we could make it optional)
 	 */
+	if (use_clamp) {
 #ifdef USE_VLA
 		double center[dims];
 #else
@@ -556,6 +562,7 @@ static void cubic_from_points(
 			imul_vn_fl(p2, sqrt(dist_sq_max) / sqrt(p2_dist_sq), dims);
 			iadd_vnvn(p2, center, dims);
 		}
+	}
 	/* end clamping */
 }