Fix #2335 (delete job flooding) (#2372)

* Fix #2335 (delete job flooding)

The problem was:

- You are offline, and an ephemeral message is due to delete.
- load_imap_deletion_job() is called and returns a deletion job for it.
- The job fails because, well, we are offline.
- The job is saved into the database.
- load_imap_deletion_job() is called again, and so on.

* Add test

src/job.rs

@@ -130,7 +130,7 @@ impl From<Action> for Thread {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Job {
     pub job_id: u32,
     pub action: Action,
@@ -1030,7 +1030,7 @@ pub(crate) enum Connection<'a> {
     Smtp(&'a mut Smtp),
 }
 
-async fn load_imap_deletion_job(context: &Context) -> sql::Result<Option<Job>> {
+pub(crate) async fn load_imap_deletion_job(context: &Context) -> sql::Result<Option<Job>> {
     let res = if let Some(msg_id) = load_imap_deletion_msgid(context).await? {
         info!(context, "verbose (issue 2335): loading imap deletion job");
         Some(Job::new(