Bug 28940: In spinelabel-print.tt call IntranetUserJS only once

Bug 28940: In spinelabel-print.tt call IntranetUserJS only once

1. In IntranetUser add some JS that will target spinelabel-print.tt, I used this:
    if ( $('#labels_spinelabel-print').length ) {
      $('#labels_spinelabel-print').append('<div>TEST</div>');
      console.log('TEST');
    }
2. Generate a quick spine label
3. Once you have entered a barcode the JS will go off 2x. With the jQuery added you will see 2 div's with the word 'TEST'. Look at the console and you will also see TEST console logged 2x.
4. Apply patch
5. Try seto 2 and 3 again, the JS should only be called once.

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>