Fix not use addOnGlobalLayoutListener to get mSelectedTab

[xingstarx]

In some devices, mSelectedTab from PageListener onPageScrolled is not always equals pager.getCurrentItem()

afater debug OnPageChangeListener onPageScrolled event. i get mSelectedTab values is only 0, 0 , 1
when I scroll the three Tab in one samsung device
but after I call notifyDataSetChanged() I get mSelectedTab = mViewPager.getCurrentItem() is 1 when the tab selected in the second Tab , is't not equals 0

and not need use addOnGlobalLayoutListener to get mSelectedTab values

mSelectedTab always record afater onPageScrolled called