Bug 8949: Trying to view help on a page without any help results in a nasty error

Bug 8949: Trying to view help on a page without any help results in a nasty error

The problem was probably a side effect of bug 7038

I've checked that things are OK in translated languages.

Test plan:
 * open help on a page with help in english (mainpage.pl)
 * open help on a page with help in another language (mainpage.pl)
=> you'll see the online help, as usual
 * open help on a page without help in english (acqui/addorderiso2709.pl)
 * open help on a page without help in another language (acqui/addorderiso2709.pl)
=> you'll get the "oops, no help available, sorry", no more the Perl error

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Passed-QA-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>