Bug 17477: Duplicating a subfield yields an empty subfield tag

Bug 17477: Duplicating a subfield yields an empty subfield tag

The problem only when clone a textareas in 5XX

Steps to reproduce error:
- On the cataloging screen (basic screen), create a new record
- Go to the 5xx fields
- Put something on the 521$a subfield or other textareas (e.g. 520$u or
 583$x)
- Clone the subfield
=> FAIL: The subfield correctly doesn't include the original data,
BUT it doesn't have the subtield tag either.

- Apply patch
- Clean cache browser and reload page
- Repeat steps above
- Verify that works as expected

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit fbe75e66ccb93a6a4d973e3066ca1ebad169a5b6)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>