[as3] Ported IKConstraint fix.

spine-as3/spine-as3/src/spine/IkConstraint.as

@@ -176,22 +176,25 @@ package spine {
 				}
 				var minAngle : Number = Math.PI, minX : Number = l1 - a, minDist : Number = minX * minX, minY : Number = 0;
 				var maxAngle : Number = 0, maxX : Number = l1 + a, maxDist : Number = maxX * maxX, maxY : Number = 0;
-				var angle : Number = Math.acos(-a * l1 / (aa - bb));
-				x = a * Math.cos(angle) + l1;
-				y = b * Math.sin(angle);
+				c = -a * l1 / (aa - bb);
+				if (c >= -1 && c <= 1) {
+					c = Math.acos(c);
+					x = a * Math.cos(c) + l1;
+					y = b * Math.sin(c);
 					d = x * x + y * y;
 					if (d < minDist) {
-					minAngle = angle;
+						minAngle = c;
 						minDist = d;
 						minX = x;
 						minY = y;
 					}
 					if (d > maxDist) {
-					maxAngle = angle;
+						maxAngle = c;
 						maxDist = d;
 						maxX = x;
 						maxY = y;
 					}
+				}
 				if (dd <= (minDist + maxDist) / 2) {
 					a1 = ta - Math.atan2(minY * bendDir, minX);
 					a2 = minAngle * bendDir;