Rekey array, or else the last field in the forms will not be shown

This error is caused by unsetting $fields[ 0 ] which is when the full name is shown first in the group.

`Notice: Undefined offset: 0 in wp-content/plugins/buddypress/bp-xprofile/bp-xprofile-template.php on line 108`

This PR patches the issue and rekeys the array so that the rewind method does what it needs to do.