[c] Fixed IK constraint NaN when a parent bone has zero scale.

spine-c/spine-c/src/spine/IkConstraint.c

@@ -84,7 +84,7 @@ void spIkConstraint_apply1(spBone *bone, float targetX, float targetY, int /*boo
 			ty = targetY - bone->worldY;
 			break;
 		case SP_TRANSFORMMODE_NOROTATIONORREFLECTION: {
-			s = ABS(pa * pd - pb * pc) / (pa * pa + pc * pc);
+			s = ABS(pa * pd - pb * pc) / MAX(0.0001f, pa * pa + pc * pc);
 			sa = pa / bone->skeleton->scaleX;
 			sc = pc / bone->skeleton->scaleY;
 			pb = -sc * s * bone->skeleton->scaleX;
@@ -94,6 +94,8 @@ void spIkConstraint_apply1(spBone *bone, float targetX, float targetY, int /*boo
 		default: {
 			float x = targetX - p->worldX, y = targetY - p->worldY;
 			float d = pa * pd - pb * pc;
+            if (d > 0) d = MAX(0.0001f, d);
+            else d = MIN(-0.0001f, d);
 			tx = (x * pd - y * pb) / d - bone->ax;
 			ty = (y * pa - x * pc) / d - bone->ay;
 		}
@@ -177,7 +179,9 @@ void spIkConstraint_apply2(spBone *parent, spBone *child, float targetX, float t
 	b = pp->b;
 	c = pp->c;
 	d = pp->d;
-	id = 1 / (a * d - b * c);
+	id = a * d - b * c;
+    if (id > 0) id = 1 / MAX(0.0001f, id);
+    else id = 1 / MIN(0.0001f, id);
 	x = cwx - pp->worldX;
 	y = cwy - pp->worldY;
 	dx = (x * d - y * b) * id - px;