Add logic to deal with forms that are owned by anonymous, uids that no longer exist

[kreynen]

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '' for key 'name': INSERT INTO {users} (uid, name, pass, mail, theme, signature, signature_format, created, access, login, status, timezone, language, picture, init, data, uuid) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9, :db_insert_placeholder_10, :db_insert_placeholder_11, :db_insert_placeholder_12, :db_insert_placeholder_13, :db_insert_placeholder_14, :db_insert_placeholder_15, :db_insert_placeholder_16); Array#012(#012 [:db_insert_placeholder_0] => 541#012 [:db_insert_placeholder_1] => #012 [:db_insert_placeholder_2] => #012 [:db_insert_placeholder_3] => #012 [:db_insert_placeholder_4] => #012 [:db_insert_placeholder_5] => #012 [:db_insert_placeholder_6] => #012 [:db_insert_placeholder_7] => 0#012 [:db_insert_placeholder_8] => 0#012 [:db_insert_placeholder_9] => 0#012 [:db_insert_placeholder_10] => 0#012 [:db_insert_placeholder_11] => #012 [:db_insert_placeholder_12] => #012 [:db_insert_placeholder_13] => 0#012 [:db_insert_placeholder_14] => #012 [:db_insert_placeholder_15] => b:0;#012 [:db_insert_placeholder_16] => 5a3e1181-f2c4-4f82-8f74-169bc69c8cc6#012)#012 in drupal_write_record() (line 7387 of /data/atlas/code/cores/drupal/drupal-7.57/includes/common.inc).