On resetting I get Password must not contain the username

When changing password I get Password must not contain the username event tho it does not.

The issue is on line 29: stripos($password, $user->getAccountName()). If $password is null or empty, stripos() in PHP 8+ will trigger a deprecation warning.

This patch fixes two issues:

• Skips password validation when the password field is empty on change_pwd_form
• Only sets username if the 'name' field exists in the form (prevents NULL username error)