Other information:
1.Since the scroll range of the container = [0 ~ scrollHeight-clientHeight],
so lastCalcIndex is never equal to lastIndex.
2.When not scrolling to the bottom, paddingTop affects the position of the real element in the viewport, but paddingBottom
does not
3.When scrolling to the bottom, paddingBottom = (last - end) * this.getEstimateSize(),
since last - end = 0, so it is the right result
What kind of this PR? (check at least one)
Other information: 1.Since the scroll range of the container = [0 ~ scrollHeight-clientHeight], so lastCalcIndex is never equal to lastIndex. 2.When not scrolling to the bottom, paddingTop affects the position of the real element in the viewport, but paddingBottom does not 3.When scrolling to the bottom, paddingBottom = (last - end) * this.getEstimateSize(), since last - end = 0, so it is the right result