Fix exception when stopping the HTTP server if already stopped.

src/utils/httpserver.py

@@ -180,6 +180,7 @@ def stopServer():
     """Stops the HTTP server. Should be run only from this module or from
     when the bot is dying (ie. from supybot.world)"""
     global httpServer
+    if httpServer is not None:
         log.info('Stopping HTTP server.')
         httpServer.shutdown()
         httpServer = None