avoid divide by 0 in getting pi simulation value

pi/models.py

@@ -59,6 +59,8 @@ class PiLog(models.Model):
     @property
     def value(self):
         """Return this log entry's estimated value of pi."""
+        if self.total_count == 0:
+            return 0.0
         return 4.0 * int(self.total_count_inside) / int(self.total_count)
 
     @property