py3: Fix swift-recon

Avoid things like

    TypeError: '<' not supported between instances of 'NoneType' and 'int'

Change-Id: I82edbf1ddcc28f86e97405d21db0b96249412eac

swift/cli/recon.py

@@ -459,6 +459,8 @@ class SwiftRecon(object):
                         stats[stat_key].append(repl_stats.get(stat_key))
                 last = response.get('replication_last',
                                     response.get('object_replication_last', 0))
+                if last is None:
+                    continue
                 if last < least_recent_time:
                     least_recent_time = last
                     least_recent_url = url