fix: Handle null reference when Voice State is still in cache, but the channel it belongs to has been expired (#1648)

Fixes #1644

Author: silasary

interactions/client/smart_cache.py

@@ -794,7 +794,7 @@ async def place_voice_state_data(
 
         if old_state := self.get_voice_state(user_id):
             # noinspection PyProtectedMember
-            if user_id in old_state.channel._voice_member_ids:
+            if old_state.channel is not None and user_id in old_state.channel._voice_member_ids:
                 # noinspection PyProtectedMember
                 old_state.channel._voice_member_ids.remove(user_id)