script: do not try to close stderr twice

script: do not try to close stderr twice

The commit cdd2a8c360c70d16804ace7cc923a6c6bb7c9ca9 broke script(1)
return value.

$ script -e -c "echo"; echo $?
1

The reason, as Daniel it reported, was that the script will close stderr
twice, once as timing file and atexit() in function close_stdout().  This
commit fixes the problem.

Reported-by: Daniel Narvaez <dwnarvaez@gmail.com>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>