fix kb entry sorting

kb/models.py

@@ -1,5 +1,6 @@
 from django.db import models
 from django.db.models.aggregates import Sum
+from django.db.models.functions import Coalesce
 from django.conf import settings
 from django.urls import reverse
 from django.template.loader import render_to_string
@@ -101,8 +102,8 @@ class KbEntry(models.Model):
     class KbEntryManager(models.Manager):
         def get_top(self, n, **kwargs):
             return (self.filter(internal=False, **kwargs)
-                    .annotate(Sum('vote_set__vote'))
-                    .order_by('-vote_set__vote__sum')
+                    .annotate(score=Coalesce(Sum('vote_set__vote'), 0))
+                    .order_by('-score', 'id')
                     [:n])
 
     objects = KbEntryManager()