[FIX] website_shift: Error when regular has no tz

Issue when no timezone set to a regular worker. It try to use the user
timezone but has it doesn't exists runs into an error.
To solve this, it first takes the timezone of the user, if it is
empty, it takes the timezone of the context, and if also empty it uses
UTC.

beesdoo_website_shift/__openerp__.py

@@ -16,7 +16,7 @@
 
     'author': 'Rémy Taymans',
     'license': 'AGPL-3',
-    'version': '9.0.2.0',
+    'version': '9.0.2.1',
     'website': "https://github.com/beescoop/Obeesdoo",
 
     'category': 'Cooperative management',

beesdoo_website_shift/controllers/main.py

@@ -45,8 +45,13 @@ class WebsiteShiftController(http.Controller):
         # Ensure that the datetime given is without a timezone
         assert datetime.tzinfo is None
         # Get current user and user timezone
+        # Take user tz, if empty use context tz, if empty use UTC
         cur_user = request.env['res.users'].browse(request.uid)
-        user_tz = timezone(cur_user.tz)
+        user_tz = utc
+        if cur_user.tz:
+            user_tz = timezone(cur_user.tz)
+        elif request.env.context['tz']:
+            user_tz = timezone(request.env.context['tz'])
         # Convert to UTC
         dt_utc = utc.localize(datetime, is_dst=False)
         # Convert to user TZ