Boundary instability issue

[martin-oy]

Hello, I'm trying to implement my own listview extending your lib. I found a problem while testing.
When you drag very slowly near/across boundary at first time, the view becomes unstable and reporting warnings on loading message textview. I found out that you omitted a very tiny condition judging in your codes.
It can be improved by modifying the onScroll() method in line 292 to 293, putting one more condition
if (mRefreshView.getBottom() < mRefreshViewHeight + 20 && mRefreshView.getTop() != 0 && mRefreshState != PULL_TO_REFRESH)
instead of
if (mRefreshView.getBottom() < mRefreshViewHeight + 20 && mRefreshState != PULL_TO_REFRESH)