When creating an account from the website (through the link "Don't have an
account?") while having been previously identified, the creation lasts a very
long time and ends-up with a http 502 error (actually a timeout). Same when
logging although being already logged.
Technical note: The problem was due to a database deadlock because of going
twice through authentication. A record was deleted in one transaction while
being written in another (_merge_visitor deletes it and _update_visitor_last
visit writes it but with different environment).
Task-2950241
closesodoo/odoo#99723
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>