ZWSP / WBR insertion causes unintended space trimming on line breaks

When a ZWSP or WBR element appears at the end of a line in source HTML, the space that should be introduced by the line break may be removed. The behavior may vary by browser. Possible solution from the BudouX side is not to insert a separator right before `\n`.

**Demo:** https://codepen.io/tushuhei/pen/GRbraYN

**HTML:**
```html

これは
テスト
です。

これは​
テスト
です。​

これは
テスト
です。