reinstante the await self in handle_comm

If not awaited, the server might server handlers before the server is
properly initialized. For instance plugins and preload modules might
not be fully loaded before that happens

distributed/core.py

@@ -438,6 +438,10 @@ async def handle_comm(self, comm):
         logger.debug("Connection from %r to %s", address, type(self).__name__)
         self._comms[comm] = op
 
+        # The server might already be listening even though it is not properly
+        # started, yet. (e.g. preload modules not done)
+        await self
+
         try:
             while True:
                 try: