enter "Home screen backup password" in "Developer Settings",
do nothings and then click "Set backup password", There will
be a toast display "New backup password set".
The new password field cannot be empty.
Bug: https://partnerissuetracker.corp.google.com/u/2/issues/111261338
Test: empty string can not be set as a password
Signed-off-by: xiamin <xiamin@xiaomi.com>
