Make scan_folders work when inbox is not watched (#2446)

When watch_inbox was off, scan_folders failed and a toast "IMAP operation attempted while it is torn down" was shown.

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The problem was:

When inbox_watch is off, scan_folders() is called at https://github.com/deltachat/deltachat-core-rust/blob/244260a9789a34c8cdd50c73b96557a8ced40345/src/scheduler.rs#L107 but connect_configured() is not called before.



* Add test

* Don't only setup handle, but connect_configured() in scan_folders()

src/imap/scan_folders.rs

@@ -25,7 +25,7 @@ impl Imap {
         }
         info!(context, "Starting full folder scan");
 
-        self.setup_handle(context).await?;
+        self.connect_configured(context).await?;
         let session = self.session.as_mut();
         let session = session.context("scan_folders(): IMAP No Connection established")?;
         let folders: Vec<_> = session.list(Some(""), Some("*")).await?.collect().await;