[FIX] utm: dont try to set cookies if Response is Exception

Also prefetch tracking_fields before the call to super to avoid to use a closed cursor.
See odoo/odoo@6780597

this commit closes #13646

addons/utm/models/ir_http.py

@@ -10,8 +10,16 @@ class ir_http(orm.AbstractModel):
         return request.httprequest.host
 
     def _dispatch(self):
+        tracked_fields = self.pool['utm.mixin'].tracking_fields()
+
         response = super(ir_http, self)._dispatch()
-        for var, dummy, cook in self.pool['utm.mixin'].tracking_fields():
+
+        # no set_cookie on Exception
+        if isinstance(response, Exception):
+            return response
+
+        for var, dummy, cook in tracked_fields:
             if var in request.params and request.httprequest.cookies.get(var) != request.params[var]:
                 response.set_cookie(cook, request.params[var], domain=self.get_utm_domain_cookies())
+
         return response