feat: throw custom error for uncached Guild#me (#3271)

* handle cases where Guild#me is uncached

* fix id prop

* remove unnecessary checks

* space's requested changes

src/structures/GuildMember.js

@@ -201,6 +201,7 @@ class GuildMember extends Base {
   get manageable() {
     if (this.user.id === this.guild.ownerID) return false;
     if (this.user.id === this.client.user.id) return false;
+    if (!this.guild.me) throw new Error('GUILD_UNCACHED_ME');
     return this.guild.me.roles.highest.comparePositionTo(this.roles.highest) > 0;
   }