Bug 25940: Check for reserve_id before Dopop

Bug 25940: Check for reserve_id before Dopop

TEST PLAN:
1. Have an item belonging to a different branch and check it in.
2. When the modal pops up hit 'Yes, print slip' or 'Print slip' if  AutomaticItemReturn is set to 'don't'
3. The first print dialog should appear with a URL like '/cgi-bin/koha/circ/transfer-slip.pl?transferitem=18&&branchcode=CPL&op=slip'
4. Close that print dialog and you will immediately see another one that says 'No slip template found'.
5. Notice the URL of the second pop-up is:  /cgi-bin/koha/circ/hold-transfer-slip.pl?reserve_id=
6. There is no reserve id so the template is not found.
7. Apply patch
8. Repeat 1-6
9. You should no longer have two print dialogs

Signed-off-by: Lisette Scheer <lisetteslatah@gmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>