Summary: Fixed: misshandled protocol disconnect during connection setup

If a protocol was disconnected while registering, maybe because the
server was still starting, the disconnection was handled correctly by
the Client, because the protocol attribute wasn't set, the connection
wasn't retried.

src/ZEO/asyncio/client.py

@@ -149,16 +149,18 @@ class Protocol(asyncio.Protocol):
         self.heartbeat(write=False)
 
     def connection_lost(self, exc):
+        logger.debug('connection_lost %r', exc)
         self.heartbeat_handle.cancel()
         if self.closed:
             for f in self.pop_futures():
                 f.cancel()
         else:
-            self.client.disconnected(self)
             # We have to be careful processing the futures, because
             # exception callbacks might modufy them.
             for f in self.pop_futures():
                 f.set_exception(ClientDisconnected(exc or 'connection lost'))
+            self.closed = True
+            self.client.disconnected(self)
 
     def finish_connect(self, protocol_version):
 
@@ -439,6 +441,7 @@ class Client:
         self.protocols = ()
 
     def disconnected(self, protocol=None):
+        logger.debug('disconnected %r %r', self, protocol)
         if protocol is None or protocol is self.protocol:
             if protocol is self.protocol and protocol is not None:
                 self.client.notify_disconnected()
@@ -447,6 +450,8 @@ class Client:
             self.connected = concurrent.futures.Future()
             self.protocol = None
             self._clear_protocols()
+
+        if all(p.closed for p in self.protocols):
             self.try_connecting()
 
     def upgrade(self, protocol):
@@ -457,6 +462,7 @@ class Client:
         self._clear_protocols(protocol)
 
     def try_connecting(self):
+        logger.debug('try_connecting')
         if not self.closed:
             self.protocols = [
                 Protocol(self.loop, addr, self,