Bug 29416: (bug 28941 follow-up) Restore suggestion prefill

Bug 29416: (bug 28941 follow-up) Restore suggestion prefill

From commit 586bed1319592e05f5dc3acf64a1dba8cae69d6b
     Bug 28941: Filter suggestion inputs at the OPAC

But later in the script we send { suggestion => %$suggestion } to the
template and so erase the variable previously passed.

Test plan:
Login at the OPAC
Go to the bibliographic detail page
Suggest for purchase
=> The form must be prefilled!

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>