fix page view bug

com.unity.uiwidgets/Runtime/widgets/page_view.cs

 
         public override bool applyViewportDimension(float viewportDimension) {
             float oldViewportDimensions = 0.0f;
-            if (haveDimensions) {
+            if (haveViewportDimension) {
                 oldViewportDimensions = this.viewportDimension;
             }
             

com.unity.uiwidgets/Runtime/widgets/scroll_position.cs

 
         float? _viewportDimension;
 
+        public bool haveViewportDimension {
+            get { return _viewportDimension != null; }
+        }
+
         public bool haveDimensions {
             get { return _haveDimensions; }
         }