[FIX] website_forum: give a name to posts created from comments
[FIX] website_forum: give a name to posts created from comments

From Odoo 13.0, the list of answers of a user displays the name of the
answer itself, and not its parent's.
Answers created directly on a question are given a name, but answers
created from a comment are not.

This commit fixes this behavior for a better consistancy: all posts
should have a displayable name.

A migration step on saas~12.5 will populate from their parent's name
the existing posts that don't have a name.

closes odoo/odoo#45193

X-original-commit: 327079e97d12bf3bfcbc74e78bcc7ebc36149d02
Signed-off-by: Paul Morelle <4950c5a1ead41dfa3dcc3f68ece6c9007ac6ccce@users.noreply.github.com>

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo