Bug 21608: Add value for 'rank-request' when dropdwn disabled

Bug 21608: Add value for 'rank-request' when dropdwn disabled

When a field is disabled no value is submitted in the form - this was
causing found holds to be reverted

To test:
1 - Apply all patches except this one
2 - PLace several holds on one bib
3 - Set at least one waiting or intransit
4 - Making no adjustments hit "Update holds"
5 - Waiting/intransit holds are all reset
6 - Mark them waiting/intransit again
7 - Apply this patch
8 - Click 'update holds'
9 - Found status is not accidentally reverted

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>