[Bug] select: nzScrollToBottom event not emited when screen zoom to 125% and data count 10

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Version
1.4.0

Environment
Win10，Chrome 66.0.3359.117，screen resolution 1920*1080 zoom to 125%

Reproduction link
https://stackblitz.com/edit/ng-zorro-antd-start-njn3wk

Steps to reproduce

1. Select componnet bind 10 options (must 10 items!)
2. use screen resolution 1920*1080 zoom to 125%
3. drop down select items and scroll to bottom, and nzScrollToBottom not emited.
4. bind 15 items or 25 items no problem. when 10 or 20 items nzScrollToBottom not emited. when screen not zoomed no problem.

What is expected?
nzScrollToBottom event emited

What is actually happening?
nzScrollToBottom not emited

Other?
when screen zoom, scrollTop has decimal part，nzScrollToBottom not emited

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temporary solution：
modify \node_modules\ng-zorro-antd\esm5\antd.js line 5353
NzOptionContainerComponent.prototype.dropDownScroll method:
if (ul && (ul.scrollHeight - ul.scrollTop === ul.clientHeight)) {

to:
if (ul && (ul.scrollHeight - Math.ceil(ul.scrollTop) === ul.clientHeight)) {

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Thanks for the excellent work！