fixed missing textField-dispose in Button; fixed text alignment gette…

…rs (refs Gamua#456)

starling/src/starling/display/Button.as

@@ -79,6 +79,15 @@ package starling.display
             this.text = text;
         }
 
+        /** @inheritDoc */
+        public override function dispose():void
+        {
+            // text field might be disconnected from parent, so we have to dispose it manually
+            mTextField.dispose();
+
+            super.dispose();
+        }
+
         private function resetContents():void
         {
             mIsDown = false;
@@ -239,15 +248,23 @@ package starling.display
         }
 
         /** The vertical alignment of the text on the button. */
-        public function get textVAlign():String { return mTextField.vAlign; }
+        public function get textVAlign():String
+        {
+            return mTextField ? mTextField.vAlign : VAlign.CENTER;
+        }
+
         public function set textVAlign(value:String):void
         {
             createTextField();
             mTextField.vAlign = value;
         }
 
         /** The horizontal alignment of the text on the button. */
-        public function get textHAlign():String { return mTextField.hAlign; }
+        public function get textHAlign():String
+        {
+            return mTextField ? mTextField.hAlign : HAlign.CENTER;
+        }
+
         public function set textHAlign(value:String):void
         {
             createTextField();