Add null check for connection to prevent AttributeError on drain_events

amqp/abstract_channel.py

@@ -96,7 +96,10 @@ def wait(self, method, callback=None, timeout=None, returns_tuple=False):
 
         try:
             while not p.ready:
-                self.connection.drain_events(timeout=timeout)
+                conn = self.connection
+                if conn is None:
+                    raise RecoverableConnectionError('connection already closed')
+                conn.drain_events(timeout=timeout)
 
             if p.value:
                 args, kwargs = p.value

t/unit/test_abstract_channel.py

@@ -83,6 +83,13 @@ def on_drain(*args, **kwargs):
             self.c.wait([(50, 61)])
             assert self.c._pending[(50, 61)] is prev
 
+    def test_wait__no_connection(self):
+        self.c.connection = None
+        with pytest.raises(RecoverableConnectionError,
+                           match='connection already closed'):
+            self.c.wait((50, 61))
+        assert (50, 61) not in self.c._pending
+
     def test_dispatch_method__content_encoding(self):
         self.c.auto_decode = True
         self.method.args = None