galaxy: ensure the club score is positive

galaxy/models.py

@@ -370,7 +370,7 @@ class Galaxy(models.Model):
                         (earliest_end - latest_start).days,
                     )
                 )
-                score += cls.CLUBS_POINTS * (earliest_end - latest_start).days
+                score += cls.CLUBS_POINTS * abs((earliest_end - latest_start).days)
         return score
 
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