[BUGFIX] Encrypt hidden field with rsaauth

Instead of encrypting the visible field, the value of
the hidden field for rsa input fields have to be encrypted.

Resolves: #70118
Releases: master
Change-Id: I369a81d8168cda33097c4e1d3a0b86d96503e4bc
Reviewed-on: http://review.typo3.org/43581


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>