Fix: now applying the same verifications when creating or editing comments

[Lucas-C]

Checklist

• All new and existing tests are passing
• (If adding features:) I have added tests to cover my changes
• [-] (If docs changes needed:) I have updated the documentation accordingly.
• [-] I have added an entry to CHANGES.rst because this is a user-facing change or an important bugfix
• I have written proper commit message(s)

What changes does this Pull Request introduce?

The same API.verify() method is called when creating a new comment or editing existing ones.
Previously, API.verify() was only called during comment creation.

Why is this necessary?

In order to face spammers, I use a custom API.verify() method on my isso instance to forbids URLs in comments
( while waiting for some other spam-control mechanism to be implemented in isso maybe on day, cf. #941 )

On my instance, I have seen spammers creating empty comments and then editing them to insert URLs.

This PR ensures that the same rules defined in API.verify() are applied during all the "life cycle" of a comment.