channels should be cleared of users when *we* part them

src/core_modules/line_handler/channel.py

@@ -106,6 +106,9 @@ def part(events, event):
             user=user, server=event["server"])
     else:
         event["server"].channels.remove(channel)
+        for user in channel.users:
+            event["server"].part_user(channel, user)
+
         events.on("self.part").call(channel=channel, reason=reason,
             server=event["server"])