If you want to edit a user within the sys_action module, you have to
set a (new) password as otherwise the record won't be updated. This
patch allows an empty password field for updates while new users
still need a defined password.

Resolves: #25700
Releases: 6.2
Change-Id: I37c20a706b15ebce458033c4f5fe4016236ef1d8
Reviewed-on: https://review.typo3.org/27377
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn