Arithmetic expansion in rediretion word is evaluated twice

[Oğuz]

See:

    $ unset foo
    $ : <$((foo+=42))
    bash: 84: No such file or directory
    $ echo $foo
    84

Reproducible on 4.4.20 and 5.0.11, couldn't try on development version
because since the last push it doesn't compile


-- 
Oğuz