Only update MARC on full entry of fixed fields

Only update MARC on full entry of fixed fields

AKA:
Lang is 3 characters long. Entering 1 character would cause focus to leave.
MARC would also update incorrectly.

This only triggers the update when the full 3 characters are entered.

This not only prevents issues with catalogers editing multi-character fixed
fields but also makes it less likely they accidentally corrupt the records.

Signed-off-by: Thomas Berezansky <tsbere@mvlc.org>
Signed-off-by: Mike Rylander <mrylander@gmail.com>