[FIX] website: check that website.user_id is not falsy

This field should be required.

This commits closes odoo#21997

@KangOl: diff in addons/website/models/ir_http.py is for existing db
It can be ignored in master because required will be apply

addons/website/models/ir_http.py

@@ -40,7 +40,7 @@ def _get_converters(self):
     def _auth_method_public(self):
         if not request.session.uid:
             website = self.pool['website'].get_current_website(request.cr, openerp.SUPERUSER_ID, context=request.context)
-            if website:
+            if website and website.user_id:
                 request.uid = website.user_id.id
             else:
                 request.uid = self.pool['ir.model.data'].xmlid_to_res_id(request.cr, openerp.SUPERUSER_ID, 'base', 'public_user')

addons/website/models/website.py

@@ -166,7 +166,7 @@ def _get_menu(self, cr, uid, ids, name, arg, context=None):
         'social_youtube': fields.char('Youtube Account'),
         'social_googleplus': fields.char('Google+ Account'),
         'google_analytics_key': fields.char('Google Analytics Key'),
-        'user_id': fields.many2one('res.users', string='Public User'),
+        'user_id': fields.many2one('res.users', string='Public User', required=True),
         'compress_html': fields.boolean('Compress HTML'),
         'cdn_activated': fields.boolean('Activate CDN for assets'),
         'cdn_url': fields.char('CDN Base URL'),