Fast Scroller works wrongly after customizing CCP Dialog theme.

Hello! I try to change the CCP Dialog size by these [two ways] (https://github.com/hbb20/CountryCodePickerProject/issues/265#issuecomment-458756357), and both of them are available, but they cause a bug too.
If the CCP Dialog size is changed and the height is not matching parent, the Fast Scroller will jump to the wrong position when user click or drag the scroller bar and cause the list jump to the wrong place.
By the way, if the CCP Dialog have the properties about size will make it better in my opinion.

首先，使用 issue #265 中链接的两种 CCP Dialog 调整大小方法重现该问题，并将对话框高度设置得小于其父元素。跟踪点击并拖动 Fast Scroller 滚动条时的行为；完成标准是，在对话框调整大小后，这两种操作都能正确定位国家列表。

由索引模型根据 Issue 内容生成。