`GatewayDispatch._handle_message_generic` assumes valid guild cache

[schlopp]

Summary

The method GatewayDispatch._handle_message_generic assumes that there is a cached guild for every message edited by a GuildMember, which could be false if the guild intent is turned off

Reproduction Steps

1. Turn off guild intent
2. Receive message edit event in a guild
3. The message's author's guild (possibly) get's cached as None (even though its typed as Guild)

Minimal Reproducible Code

async def _handle_message_generic(
            self,
            data: payloads.Message) -> tuple[Message | None, Message] | None:
        """Handle message create and message edit."""

        # If there's no author, it's a webhook message
        if "author" not in data:
            return None

        # Get a message from cache (in case it's an edit or delete)
        cached = self.cache.get_message(data["id"])
        if cached is not None:
            current = copy(cached)
            message = cached._update(data)  # because a message already existed we don't need to add it to cache

            # If we got here, then a new author will not be created by the message,
            # so we're going to update the cache with our new data, as well as
            # write back some of our cached items into the object
            if isinstance(message.author, GuildMember):
                assert "member" in data
                assert "guild_id" in data
                message.author._update(data["member"])
                message.author._user._update(data["author"])
                guild = self.cache.get_guild(data["guild_id"])
                message.guild = guild
                message.author.guild = guild
            else:
                message.author._update(data["author"])

        # Create a new message
        # Doing this will try and read from cache, but afterwards will create
        # new objects (of things like User, GuildMember, and Channel).
        # If new objects are made, then we want to write these back to the
        # cache (apart from Channel, which isn't a full object).
        else:
            current = None
            message = Message(state=self.parent, data=data)
            self.cache.add_messages(message)  # message to cache

        return current, message

Expected Results

I expected message.author.guild not to be None

Actual Results

I expected message.author.guild (possibly) becomes None

Intents

no guilds intent

System Information

latest version of the rewrite branch

Checklist

• I have searched the open issues for duplicates.
• I have shown the entire traceback, if possible.
• I have removed my token from display, if visible.

Additional Context

The issue takes place here