[BUGFIX] changing FE user password updates tstamp

When an FE user changes his/her password the tstamp field of the
record is also updated to reflect that the record is changed.

Change-Id: I6907c7af6c46612f5e1d2e6aca6a38e9216d3af3
Fixes: #48685
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/21186
Reviewed-by: Thomas Maroschik
Tested-by: Thomas Maroschik
Reviewed-by: Steffen Müller
Tested-by: Steffen Müller
Reviewed-on: https://review.typo3.org/21188