Fixed uncaught divbyzero wrapped in a lock which was causing a periodic deadlock

Author: Dave Rawks

memcached/python_modules/memcached.py

@@ -106,7 +106,10 @@ def metric_of(self, name):
             if name in self.last_metric:
                 num = self.metric[name]-self.last_metric[name]
                 period = self.metric[mp+"_time"]-self.last_metric[mp+"_time"]
-                val = num/period
+                try:
+                    val = num/period
+                except ZeroDivisionError:
+                    val = 0
             _Lock.release()
         elif name in self.metric:
             _Lock.acquire()