Fixed an oversight

Author: Taaku18

cogs/plugins.py

@@ -64,7 +64,7 @@ async def download_initial_plugins(self):
                 except DownloadError as exc:
                     msg = f'{parsed_plugin[0]}/{parsed_plugin[1]} - {exc}'
                     logger.error(error(msg))
-        await async_all(env() for env in self.bot.extra_events['on_plugin_ready'])
+        await async_all(env() for env in self.bot.extra_events.get('on_plugin_ready', []))
         logger.debug(info('on_plugin_ready called.'))
 
     async def download_plugin_repo(self, username, repo):