Dead lock when printing objects with *print-circle*

[Affonso-Gui]

How to reproduce:

(setq c (instance object))
(setq *print-circle* t)
c
;; dead lock

What is happening:

1. prinx
2. mutex_lock to keep mark&unmark together (https://github.com/euslisp/EusLisp/blob/master/lisp/c/printer.c#L622-L630)
3. prin1
4. send obj :prin1 (https://github.com/euslisp/EusLisp/blob/master/lisp/c/printer.c#L589)
5. format ... (https://github.com/euslisp/EusLisp/blob/master/lisp/l/object.l#L15-L20)
6. prinx
7. dead lock

Not really sure how we should solve this... 🤔