[BUGFIX] Fluid: form.hidden ViewHelper needs to respect submitted data

As hidden fields might be modified via e.g. JavaScript
they also have to respect submitted data upon submit.

Change-Id: I3c0520e98bf49e80009cb6d42f9356b37bc42032
Resolves: #71301
Releases: master
Reviewed-on: https://review.typo3.org/44529


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Sebastian Fischer <typo3@evoweb.de>
Tested-by: Sebastian Fischer <typo3@evoweb.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>