fix(ios): prevent onScroll method to divide by 0 (#208)

Author: gabrielbull

ios/ReactNativePageView.m

@@ -325,9 +325,13 @@ - (void)scrollViewDidScroll:(UIScrollView *)scrollView {
     CGPoint point = scrollView.contentOffset;
     float offset = 0;
     if (self.orientation == UIPageViewControllerNavigationOrientationHorizontal) {
-        offset = (point.x - self.frame.size.width)/self.frame.size.width;
+        if (self.frame.size.width != 0) {
+            offset = (point.x - self.frame.size.width)/self.frame.size.width;
+        }
     } else {
-        offset = (point.y - self.frame.size.height)/self.frame.size.height;
+        if (self.frame.size.height != 0) {
+            offset = (point.y - self.frame.size.height)/self.frame.size.height;
+        }
     }
     if(fabs(offset) > 1) {
         offset = offset > 0 ? 1.0 : -1.0;