[csharp] Port of commit e04e7b5. Adjusted fix for IK constraint NaN when parent has zero scale.

spine-csharp/src/IkConstraint.cs

@@ -182,9 +182,14 @@ namespace Spine {
 			}
 			default: {
 				float x = targetX - p.worldX, y = targetY - p.worldY;
-				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;
+				float d = pa * pd - pb * pc;
+				if (Math.Abs(d) <= 0.0001f) {
+					tx = 0;
+					ty = 0;
+				} else {
+					tx = (x * pd - y * pb) / d - bone.ax;
+					ty = (y * pa - x * pc) / d - bone.ay;
+				}
 				break;
 			}
 			}
@@ -256,7 +261,8 @@ namespace Spine {
 			b = pp.b;
 			c = pp.c;
 			d = pp.d;
-			float id = 1 / Math.Max(0.0001f, a * d - b * c), x = cwx - pp.worldX, y = cwy - pp.worldY;
+			float id = a * d - b * c, x = cwx - pp.worldX, y = cwy - pp.worldY;
+			id = Math.Abs(id) <= 0.0001f ? 0 : 1 / id;
 			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) {