[IMP] http: rollback from checked_call only if necessary

The rollback clears the cache, which lose all data that have been fetched before
arriving in the route method.

This lost cache includes some website data that was used during the dispatch and
that will be used again in the route.

By keeping it we reduce the number of queries on every request by at least 2.

Part of task-2061122

closes odoo/odoo#36245

Signed-off-by: Raphael Collet (rco) <rco@openerp.com>

odoo/http.py

@@ -331,14 +331,18 @@ class WebRequest(object):
         if self.endpoint.first_arg_is_req:
             args = (request,) + args
 
+        first_time = True
+
         # Correct exception handling and concurency retry
         @service_model.check
         def checked_call(___dbname, *a, **kw):
+            nonlocal first_time
             # The decorator can call us more than once if there is an database error. In this
             # case, the request cursor is unusable. Rollback transaction to create a new one.
-            if self._cr:
+            if self._cr and not first_time:
                 self._cr.rollback()
                 self.env.clear()
+            first_time = False
             result = self.endpoint(*a, **kw)
             if isinstance(result, Response) and result.is_qweb:
                 # Early rendering of lazy responses to benefit from @service_model.check protection