Special entities in entities_additional may break escaping

[Deroin]

Type of report

Bug

Provide detailed reproduction steps (if any)

1. Initialize CKE with entities_additional set to 'apos'
2. Enter text amp' into the editor
3. Switch to source view

Expected result

Source view shows <p>amp&apos;</p>

Actual result

Source view shows <p>&undefined;&undefined;&undefined;&apos;</p>

Other details

• Browser: Firefox, Chrome
• OS: Debian, Windows
• CKEditor version: 4.10.1
• Installed CKEditor plugins: Default plugins as in development version

I pinned this down to be caused by plugins/entities/plugin.js::buildTable. During the replacement of entities in line 63 any special entity will be removed from the entities list together with the following ,. If there is no comma (because it is the last value) the resulting ends with a comma.

This causes entities.split(...) to create an array with empty string as last value while the join then creates a string ending with &; which will be replaced by &; when reading inner HTML.
Due to this a, m and p will be interpreted as entities by CKE.

[msamsel]

I was able to reproduce the issue here: https://codepen.io/msamsel/pen/GYpEvv

[mlewand]

Closed wrong issue, reopening.