[BUGFIX] Incorrect display of Flexform UTF8 labels

UTF8 labels and options are displayed incorrectly in Flexforms.

Change-Id: I857bd26b8d1ee27b823e27ce5f67298f5549dc70
Resolves: #28952, #29067
Releases: 4.6, 4.5
Reviewed-on: http://review.typo3.org/6208
Reviewed-by: Tolleiv Nietsch
Tested-by: Tolleiv Nietsch
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers