[FIX] dispatch: creating a registry can raise an operational error

If you try to create a registry of a database, an exception can be
raised if the database does not exist. This may happen if you just
drop a database.

odoo/http.py

@@ -1450,8 +1450,8 @@ class Root(object):
             with request:
                 db = request.session.db
                 if db:
-                    odoo.registry(db).check_signaling()
                     try:
+                        odoo.registry(db).check_signaling()
                         with odoo.tools.mute_logger('odoo.sql_db'):
                             ir_http = request.registry['ir.http']
                     except (AttributeError, psycopg2.OperationalError, psycopg2.ProgrammingError):