Let modules suppress messages by returning None

http2irc.py

@@ -1029,6 +1029,9 @@ class WebServer:
 			except Exception as e:
 				self.logger.error(f'Bad request {id(request)}: exception in module process function: {type(e).__module__}.{type(e).__name__}: {e!s}')
 				raise aiohttp.web.HTTPBadRequest()
+			if message is None:
+				self.logger.info(f'Accepted request {id(request)}, module returned None')
+				raise aiohttp.web.HTTPOk()
 			if '\r' in message or '\n' in message:
 				self.logger.error(f'Bad request {id(request)}: module process function returned message with linebreaks: {message!r}')
 				raise aiohttp.web.HTTPBadRequest()