non continuable condition should not return

[Takashi Kato]

This should not return

(with-exception-handler
 (lambda (k) (display k) (newline))
 (lambda ()
   (with-exception-handler
    (lambda (k) #t)
    (lambda ()
      (raise 'a)))))
(display 'ng) (newline)

But displays ng

[Takashi Kato]

Don't return parent handler value on Sg_VMThrowException when is't not continuable. (Fixes #190)

→ <<cset 241200b7b7a4>>