Move the checks for the existence of the user and the presence of
their email address before the 'SpecialPasswordResetOnSubmit' hook,
instead of after. This allows extensions to make their own decisions
about whether a user exists or has email.
This also means that extensions must now check the 'requireemail'
preference when only the username is provided. They already had to
check it when only the email was provided, so this seems more like a
bug fix. To allow them to check this logic, if both the username and
email were provided by the user, provide both of them to the hook.
Bug: T151012
Change-Id: I6baf2c5194f981803198729f59e1e83d5644383a
