Fix display of monitor list if no monitor defined

It is possible that some older, predefined load balancers may
not have any monitor defined. This fixes the output (empty values
are better than an error message).

Change-Id: Ic7719811366f79c3dbe4ab7011ceac5b6c22501d

libraclient/libraapi.py

@@ -221,7 +221,7 @@ class LibraAPI(object):
         column_names = ['Type', 'Delay', 'Timeout', 'Attempts', 'Path']
         columns = ['type', 'delay', 'timeout', 'attemptsBeforeDeactivation',
                    'path']
-        self._render_dict(column_names, columns, body)
+        self._render_dict(column_names, columns, body or {})
 
     def monitor_modify_lb(self, args):
         data = {}