The commit: 75069ff179
allows users to remove their primary group, but this introduced a bug
where if you were to edit any other profile info like location or
website which is a form on a separate page then the flair dropdown,
would cause the selected flair to be removed.
This fix ensures that if the `primary_group_id` parameter is missing
from the update payload it does not remove the existing
`primary_group_id`. It will only remove the `primary_group_id` if it is
present in the payload and empty.
bd49d4af1a