<details></details> with empty line are not rendered properly

[arcturus140]

Current behavior

<details>
aaa
bbb
</details>

is ok (appropriately collapsed) but

<details>

aaa
bbb
</details>

is not working.

Related: #1674

Expected behavior

support empty lines between <details> and </details>

Steps to reproduce

1. create markdown note
2. insert above HTML
3. compare 1st and 2nd in the preview

Environment

• Version : 0.11.12
• Version : 0.11.17
• Version : 0.12.0
• OS Version and name : 16.04 Ubuntu