user-accounts: Correctly hide password mismatch warnings

The logic for the password mismatch warnings didn't handle the case where
you deleted both the passwords - it would still show them as not
matching.

Fix this by handling the three cases:
- Passwords are different
- Passwords are the same
- No passwords entered
8 jobs for user-accounts-password-match-label in 6 minutes and 56 seconds (queued for 102 minutes and 36 seconds)
Status Job ID Name Coverage
  Build
passed #62154
build

00:01:59

 
  Test
passed #62157
allowed to fail
asan

00:01:51

passed #62156
coverage

00:02:16

passed #62155
test

00:00:49

 
  Extra
manual #62160
allowed to fail manual
msan
manual #62158
allowed to fail manual
tsan
manual #62159
allowed to fail manual
ubsan
 
  Delivery
manual #62161
allowed to fail manual
packaging