[csharp] Port of commit 3fd5ed22 - Fixed IK constraint NaN when a parent bone has zero scale.

spine-csharp/src/IkConstraint.cs

@@ -172,7 +172,7 @@ namespace Spine {
 				ty = targetY - bone.worldY;
 				break;
 			case TransformMode.NoRotationOrReflection: {
-				float s = Math.Abs(pa * pd - pb * pc) / (pa * pa + pc * pc);
+				float s = Math.Abs(pa * pd - pb * pc) / Math.Max(0.0001f, pa * pa + pc * pc);
 				float sa = pa / bone.skeleton.ScaleX;
 				float sc = pc / bone.skeleton.ScaleY;
 				pb = -sc * s * bone.skeleton.ScaleX;
@@ -182,7 +182,7 @@ namespace Spine {
 			}
 			default: {
 				float x = targetX - p.worldX, y = targetY - p.worldY;
-				float d = pa * pd - pb * pc;
+				float d = Math.Max(0.0001f, pa * pd - pb * pc);
 				tx = (x * pd - y * pb) / d - bone.ax;
 				ty = (y * pa - x * pc) / d - bone.ay;
 				break;
@@ -256,7 +256,7 @@ namespace Spine {
 			b = pp.b;
 			c = pp.c;
 			d = pp.d;
-			float id = 1 / (a * d - b * c), x = cwx - pp.worldX, y = cwy - pp.worldY;
+			float id = 1 / Math.Max(0.0001f, a * d - b * c), x = cwx - pp.worldX, y = cwy - pp.worldY;
 			float dx = (x * d - y * b) * id - px, dy = (y * a - x * c) * id - py;
 			float l1 = (float)Math.Sqrt(dx * dx + dy * dy), l2 = child.data.length * csx, a1, a2;
 			if (l1 < 0.0001f) {