Bug 19798: Fix print transfer slip

Bug 19798: Fix print transfer slip

... and maybe other bugs as well
What happens here is that $itemnumber is no longer set when barcode is
passed.

Test plan:
1. Check in available/not on hold item at a non owning library.
2. Click print slip
3. Item's info must be displayed on the slip

Signed-off-by: Björn Nylén <bjorn.nylen@ub.lu.se>
Signed-off-by: Björn Nylén <bjorn.nylen@ub.lu.se>
Signed-off-by: Jon Knight <J.P.Knight@lboro.ac.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>