Fix neighbors fetching in user stories

* Order the received queryset if it doesn't have ordering.
* Do not order UserStory model by "ref" because the query:
  `queryset.filter(Q(project__gt=1) | Q(order__gt=2) | Q(ref__gt=26))`
  give the wrong result. We need to use the query:
  `queryset.filter(Q(project__gt=1) | Q(order__gt=2))`
  because in SQL there's no short-circuiting.

taiga/base/models.py

@@ -22,12 +22,14 @@ class NeighborsMixin:
         """
         if queryset is None:
             queryset = type(self).objects.get_queryset()
+        if not self._get_queryset_order_by(queryset):
+            queryset = queryset.order_by(*self._meta.ordering)
         queryset = queryset.filter(~Q(id=self.id))
 
         return self._get_previous_neighbor(queryset), self._get_next_neighbor(queryset)
 
     def _get_queryset_order_by(self, queryset):
-        return queryset.query.order_by or [self._meta.pk.name]
+        return queryset.query.order_by or []
 
     def _field(self, field):
         return getattr(self, field.lstrip("-"))
@@ -57,6 +59,7 @@ class NeighborsMixin:
     def _get_next_neighbor(self, queryset):
         conds = [{"{}__{}".format(*self._filter(field, "gt", "lt")): self._field(field)}
                  for field in self._get_queryset_order_by(queryset)]
+
         try:
             return queryset.filter(self._or(conds))[0]
         except IndexError:

taiga/projects/userstories/models.py

@@ -100,7 +100,7 @@ class UserStory(NeighborsMixin, WatchedMixin, BlockedMixin, models.Model):
     class Meta:
         verbose_name = "user story"
         verbose_name_plural = "user stories"
-        ordering = ["project", "order", "ref"]
+        ordering = ["project", "order"]
         unique_together = ("ref", "project")
         permissions = (
             ("view_userstory", "Can view user story"),