launchpad/gerrit sync script doesn't set email correctly

Some launchpad imported accounts don't get email.

At least one potential cause is the import script produces account_external_ids entries that look like this:

 account_id | email_address | password | external_id
 -----------+---------------------+----------+----------------------------------------
 1216 | <email address hidden> | NULL | https://login.launchpad.net/+id/bar
 1216 | NULL | NULL | username:foo

but a correct account looks like:

 account_id | email_address | password | external_id
 -----------+---------------------------+----------+----------------------------------------
 1 | <email address hidden> | NULL | https://login.launchpad.net/+id/bar
 1 | NULL | NULL | username:foo
 1 | <email address hidden> | NULL | mailto:<email address hidden>