Make it more failsafe

application/migrations/044_add_key_to_lotw_certs.php

@@ -10,12 +10,15 @@ class Migration_add_key_to_lotw_certs extends CI_Migration {
             'cert_key TEXT',
         );
 
-
+        if (!$this->db->field_exists('cert_key', 'lotw_certs')) {
             $this->dbforge->add_column('lotw_certs', $fields);
         }
+    }
 
     public function down()
     {
+        if ($this->db->field_exists('cert_key', 'lotw_certs')) {
             $this->dbforge->drop_column('lotw_certs', 'cert_key');
         }
     }
+}