Correct an issue with events type name (unattended _ in the name)

glances/events_list.py

@@ -271,6 +271,7 @@ class GlancesEventsList:
                 event_time, event_index, event_state, event_type, event_value, proc_list, proc_desc, global_message
             )
 
+        # logger.info(self.events_list)
         return self.len()
 
     def _create_event(self, event_time, event_state, event_type, event_value, proc_desc, global_message):

glances/plugins/plugin/model.py

@@ -669,9 +669,9 @@ class GlancesPluginModel:
     def get_stat_name(self, header=None, action_key=None):
         """Return the stat name with an optional header and action_key"""
         ret = self.plugin_name
-        if header is not None:
+        if header is not None and header != '':
             ret += '_' + header
-        if action_key is not None:
+        if action_key is not None and action_key != '':
             ret += '_' + action_key
         return ret