Fix the bug the refresh view frame is incorrect.

bug repeat sequence:
1. set scroll view content inset to a nonzero number.
2. call - (void)setPullToRefreshWithHeight:(CGFloat)height actionHandler:(void (^)(BMYPullToRefreshView *pullToRefreshView))actionHandler;
3. set pullToRefreshView.preserveContentInset to "NO".
The refresh view frame is incorrect.