Cannot save an episode with the same name as a previous one

Describe the bug

After deleting an episode, it is impossible to recreate another one with the same name.

Steps to reproduce

1. Delete an episode
2. Create a new episode using the same name on ./cp-admin/podcasts/1/episodes/new
3. Hit the save button
4. Snag

Expected behavior

The episode should be saved, or the system should warn the user that the episode already exists.

Actual behavior

The deleted episode has been soft deleted. So, it is kept in the database and the new episode has the same slug as the old one. The slug field having a unique constraint, it breaks.

Relevant logs and/or screenshots

mysqli_sql_exception #1062
Duplicate entry '2-episode-i' for key 'cp_episodes.podcast_id_slug'
SYSTEMPATH/Database/MySQLi/Connection.php at line 329

322             if ($res = $this->connID->store_result())
323             {
324                 $res->free();
325             }
326         }
327         try
328         {
329             return $this->connID->query($this->prepQuery($sql));
330         }
331         catch (mysqli_sql_exception $e)
332         {
333             log_message('error', $e->getMessage());
334 
335             if ($this->DBDebug)
336             {

Context

• Castopod: alpha.51
• OS: Mac OS 10.13.6
• Browser: firefox 87.0
• Web server: OVH mutu / sql 5.2

Possible fixes

[If you can, link to the line of code that might be responsible for the problem]