Fix double folding on e-mail headers

> Ref: https://jira.ez.no/browse/EZP-23389

When setting a from/cc/bcc header with a very long name, and using a charset different than the default one (e.g. `utf-8`), headers will be double folded: once by `ezcMailTools::composeEmailAddress()`, and once by `ezcMailHeaderFolder::foldAny()` (triggered from `ezcMailPart::generateHeaders()`).

Line length won't change, but double line break will appear, making the whole e-mail invalid.

This patch fixes it, a unit test was added.