Fix multiple anchors bug

[hemml]

The bug causes anchors to be defined multiple times in some cases when *print-circle* is T:

(let ((*print-circle* t)(x '(1 2 3))) (print `(1 2 3 ,x 4 5 ,x ,x)))

(1 2 3 #2=(1 2 3) 4 5 #2=(1 2 3) #2=(1 2 3)) 

[kchanqvq]

Thanks!