NULL dereference on tag DELETE for missing or invalid tag id

The tag delete handler used short-circuit evaluation for the lookup, then accessed `original.guildId` unconditionally — yielding 500 on already-deleted tags or non-numeric ids.

The tag delete handler used short-circuit evaluation for the lookup and then accessed original.guildId unconditionally, yielding a 500 response (instead of 404) on already-deleted tags or non-numeric ids.