Test if contextual company id is positive before using it to get the timezone

Closes #13702
(grafted from fc47e80f9d10faaca8d4704f5a0c5b6765f5d9aa)

--HG--
branch : 6.0

modules/company/ir.py

@@ -39,7 +39,7 @@ class Date(metaclass=PoolMeta):
         pool = Pool()
         Company = pool.get('company.company')
         company_id = Transaction().context.get('company')
-        if timezone is None and company_id:
+        if timezone is None and company_id is not None and company_id >= 0:
             company = Company(company_id)
             if company.timezone and pytz:
                 timezone = pytz.timezone(company.timezone)