Bug 25459: Makes barcode position respect units in patron cards layout

Bug 25459: Makes barcode position respect units in patron cards layout

When using any unit besides postscript points, barcode positionning
doesn't work correctly. There is an error in the calculation: the unit
factor must be applied to the individual card part only and not to the
full page position.

This patch moves the unit part of the calculation to the right place.

To test :
1. Create a working patron card setup, using postscript points:
    card template, layout and card batch. Use barcode and at least
    one other element (text or images) in the layout.
    => Some tips for testing:
        - activate guides for the layout
        - use a template and a batch containing more than one card; the
        displacement will be different for each card and depend on the
        barcode position relative to the bottom left of the entire page.
2. Change units from postscript points to any other unit.
    => At least for the layout, but changing it in the template will
    scale the page as well.
4. Export the card batch.
3. Note the guides are scaled to fit the new unit and the lower left
corner of text and images are still correctly placed relative to the
guides, but the barcode is not.
    => In some cases, the barcode even seem to not print at all since
    it's new coordinates are out of screen.
4. Apply patch.
5. Generate the batch again.
6. Note the barcode now appears exactly where it should.

Signed-off-by: George Veranis <gveranis@dataly.gr>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>