[BUGFIX] Fix append and prepend function of valuePicker

valuePicker appends and prepends now in the correct order.

Change-Id: Ic97b8a66469d43d9269f67f1de3f0cb40d1e8321
Resolves: #79937
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/51779


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Sascha Egerer <sascha@sascha-egerer.de>
Tested-by: Sascha Egerer <sascha@sascha-egerer.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>