Bug 29511: Sort hash keys

Bug 29511: Sort hash keys

This code exists in authorities/authorities.pl and the hash keys are sorted
I just do the same here

To test:
1 - Find/create a record with 245a 245h populated
2 - Load/reload the record several times and note that fields c and b are ordered randomly
3 - Apply patch
4 - Reload and note c and b are ordered alphabetically
5 - Move subfield h before subfield c
6 - Save and reload
7 - Confirm that existing/filled fields retain order in the MARC record

Signed-off-by: Hayley Pelham <hayleypelham@catalyst.net.nz>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>