fix a display issue in the karma key score

this would probably only matter if adding a key manually that doesn't
have a score, but a fix is a fix

Signed-off-by: Brian S. Stephan <bss@incorporeal.org>

karma/models.py

@@ -1,14 +1,13 @@
 """Karma logging models."""
 
-from datetime import timedelta
 import logging
+from datetime import timedelta
+
 import pytz
-
-from irc.client import NickMask
-
 from django.conf import settings
 from django.db import models
 from django.utils import timezone
+from irc.client import NickMask
 
 log = logging.getLogger('karma.models')
 
@@ -44,12 +43,13 @@ class KarmaKey(models.Model):
     objects = KarmaKeyManager()
 
     def __str__(self):
-        """String representation."""
+        """Display the karma key and score."""
         return "{0:s} ({1:d})".format(self.key, self.score())
 
     def score(self):
         """Determine the score for this karma entry."""
-        return KarmaLogEntry.objects.filter(key=self).aggregate(models.Sum('delta'))['delta__sum']
+        score = KarmaLogEntry.objects.filter(key=self).aggregate(models.Sum('delta'))['delta__sum']
+        return score if score else 0
 
     def rank(self):
         """Determine the rank of this karma entry relative to the others."""