Audit strlen() in append_extra_args_ascii() as well.

Similar code, similar bugs.

Signed-off-by: Peter Jones <pjones@redhat.com>
Make add_extra_args_file() work properly.

Two things:
1) make it actually return the data
2) _ascii() and _unicode() will get invoked in some cases, and they need
   to handle the case where they do nothing.

Signed-off-by: Peter Jones <pjones@redhat.com>