fixed issue where MaterialLayer would break when initializing with an empty layer.

Source/ImageCardView.swift

@@ -548,7 +548,7 @@ public class ImageCardView : MaterialPulseView {
 		if nil == imageLayer {
 			imageLayer = CAShapeLayer()
 			imageLayer!.masksToBounds = true
-			imageLayer!.zPosition = -1
+			imageLayer!.zPosition = 0
 			visualLayer.addSublayer(imageLayer!)
 		}
 	}

Source/MaterialButton.swift

@@ -458,7 +458,7 @@ public class MaterialButton : UIButton {
 	//	:name:	prepareVisualLayer
 	//
 	internal func prepareVisualLayer() {
-		visualLayer.zPosition = -1
+		visualLayer.zPosition = 0
 		visualLayer.masksToBounds = true
 		layer.addSublayer(visualLayer)
 	}

Source/MaterialLayer.swift

@@ -187,7 +187,7 @@ public class MaterialLayer : CAShapeLayer {
 		shape = .None
 		shadowDepth = .None
 		super.init(coder: aDecoder)
-		prepareLayer()
+		prepareVisualLayer()
 	}
 	
 	/**
@@ -196,8 +196,8 @@ public class MaterialLayer : CAShapeLayer {
 	public override init(layer: AnyObject) {
 		shape = .None
 		shadowDepth = .None
-		super.init(layer: layer)
-		prepareLayer()
+		super.init()
+		prepareVisualLayer()
 	}
 	
 	/**
@@ -207,7 +207,7 @@ public class MaterialLayer : CAShapeLayer {
 		shape = .None
 		shadowDepth = .None
 		super.init()
-		prepareLayer()
+		prepareVisualLayer()
 	}
 	
 	/**
@@ -269,12 +269,12 @@ public class MaterialLayer : CAShapeLayer {
 	}
 	
 	/**
-		:name:	prepareLayer
+		:name:	prepareVisualLayer
 	*/
-	public func prepareLayer() {
+	public func prepareVisualLayer() {
 		// visualLayer
+		visualLayer.zPosition = 0
 		visualLayer.masksToBounds = true
-		visualLayer.zPosition = -1
 		addSublayer(visualLayer)
 	}
 	

Source/MaterialView.swift

@@ -397,7 +397,7 @@ public class MaterialView : UIView {
 	//	:name:	prepareVisualLayer
 	//
 	internal func prepareVisualLayer() {
-		visualLayer.zPosition = -1
+		visualLayer.zPosition = 0
 		visualLayer.masksToBounds = true
 		layer.addSublayer(visualLayer)
 	}