pkg_edit.php: rowhelper data not preserved on validation error
e.g.: Install pfBlockerNG and visit pkg_edit.php?xml=/pfblockerng/pfblockerng_v4lists.xml&id=2
Add an IPV4 list source on the IPV4 tab and click save. An error is reported (as it should be) but the list source is lost and has to be re-entered.
THis is true of all XML that make use of the rowhelper control.
Fixed #6577 - Preserve user input on error
(cherry picked from commit a654d899cd5d288501fea1ec52dba2e3f0e479ba)