Use guild_id instead of inspecting guild

Previously, this line caused guild-specific commands to not
execute in guilds with the applications.commands scope. In this case,
SlashContext.guild is None and SlashContext.guild_id has the guild id.

This appears to be a holdover from pre-1.0.9 when SlashContext.guild
represented either a guild or a guild id.

Author: MichaelJHarvey

discord_slash/client.py

@@ -722,11 +722,8 @@ async def on_socket_response(self, msg):
 
             selected_cmd = self.commands[to_use["data"]["name"]]
 
-            if selected_cmd.allowed_guild_ids:
-                guild_id = ctx.guild.id if isinstance(ctx.guild, discord.Guild) else ctx.guild
-
-                if guild_id not in selected_cmd.allowed_guild_ids:
-                    return
+            if selected_cmd.allowed_guild_ids and ctx.guild_id not in selected_cmd.allowed_guild_ids:
+                return
 
             if selected_cmd.has_subcommands and not selected_cmd.func:
                 return await self.handle_subcommand(ctx, to_use)