Bug 26875: Allow printing of just one barcode in batch

Bug 26875: Allow printing of just one barcode in batch

To test:
1- go to the Print Barcode Range page
2- enter From=1 and To=1
3- confirm error "Must be greater than from value."
4- apply patch, restart, reload page
5- enter From=1, To=1
6- confirm no error
7- change From to 2, error reappears

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>