Ignores scroll events while update from server is in progress (#11454)

When ItemSetChange event occurs, it will recreate the rows in client side.
This will mess up the scroll position in scrollBodyPanel when its content
is removed. This why the onScroll events should be ignored until
the scroll position is reset by lazyScroller.

Change-Id: Ib70e0dd7b730d4745a84742509145658e35d517e