./script doesn't work in completion function

[Oğuz]

See:

    $ echo echo foo bar >s
    $ chmod +x s
    $ f(){ COMPREPLY=($(bash ./s));}
    $ complete -F f g
    $
    $ g
    bar  foo
    $ g ^C
    $
    $ f(){ COMPREPLY=($(./s));}
    $ g             ^C^C
    $

I press tab after typing `g ' in both cases, this moves the cursor to
the right in the second case instead of showing the completion
options.

This is reproducible on both the devel branch and 5.1.16, I didn't test 5.2.

Oğuz