flexible-vector-delete! raises an error when removing the last element

[Takashi Kato]

This should not raise an error:

(define fv (make-flexible-vector 1 'ok))
(flexible-vector-delete! fv 0)

[Takashi Kato]

Fixing one element deletion of flexible vector (Fixes #257)

→ <<cset 8428267caf9f>>

[Takashi Kato]

This should not raise an error:

(define fv (make-flexible-vector 1 'ok))
(flexible-vector-delete! fv 0)