Prevent shy space from being added multiple times

[MarionLeHerisson]

I sometimes use JoliTypo to fix a text which has already been fixed before. If my text contains Personnalisation, after multiple saves, as many ­ will be added, which ends up giving me this kind of content :

Person­­­­­­­­na­­­­­­­­li­­­­­­­­sa­­­­­­­­tion

A lazy solution would be to replace (with regexp) ­­ with ­.

Todo :

• [ ] Check if this is happening with other fixers
• [ ] Check if this is du to JoliTypo or org_heigl/hyphenator