s modifier have problems with multibyte strings

When using %s[2,4]|givenName% for instance with givenName = Valérie, only 3 characters will be returned because «é» is seen as 2 characters my substr. We must use mb_substr instead.

(from redmine: issue id 5381, created on 2017-02-09, closed on 2017-02-09)

• Changesets:
  • Revision d867216c by Côme Chilliet on 2017-02-09T12:14:13.000Z:

Fixes #5381 Fixed s modifier for accented characters