fix: Imap::configure_mvbox: Do select_with_uidvalidity() before return

Before moving emails to the mvbox we need to remember its UIDVALIDITY, otherwise emails moved before
that wouldn't be fetched but considered "old" instead.

Also:
- Don't use `session.create()` to create mvbox as `select_with_uidvalidity()` already creates mvbox
  on its own.
- Don't try to create compat folders like "INBOX.DeltaChat", but only look for them.

src/imap.rs

@@ -1775,7 +1775,7 @@ impl Imap {
     /// Attempts to configure mvbox.
     ///
     /// Tries to find any folder in the given list of `folders`. If none is found, tries to create
-    /// any of them in the same order. This method does not use LIST command to ensure that
+    /// `folders[0]`. This method does not use LIST command to ensure that
     /// configuration works even if mailbox lookup is forbidden via Access Control List (see
     /// <https://datatracker.ietf.org/doc/html/rfc4314>).
     ///
@@ -1804,24 +1804,28 @@ impl Imap {
                     "MVBOX-folder {:?} successfully selected, using it.", &folder
                 );
                 session.close().await?;
+                // Before moving emails to the mvbox we need to remember its UIDVALIDITY, otherwise
+                // emails moved before that wouldn't be fetched but considered "old" instead.
+                self.select_with_uidvalidity(context, folder).await?;
                 return Ok(Some(folder));
             }
         }
 
-        if create_mvbox {
+        if !create_mvbox {
-            for folder in folders {
+            return Ok(None);
-                match session.create(&folder).await {
+        }
-                    Ok(_) => {
+        let Some(folder) = folders.first() else {
-                        info!(context, "MVBOX-folder {} created.", &folder);
+            return Ok(None);
-                        return Ok(Some(folder));
+        };
-                    }
+        match self.select_with_uidvalidity(context, folder).await {
-                    Err(err) => {
+            Ok(_) => {
-                        warn!(context, "Cannot create MVBOX-folder {:?}: {}", &folder, err);
+                info!(context, "MVBOX-folder {} created.", folder);
-                    }
+                return Ok(Some(folder));
-                }
+            }
+            Err(err) => {
+                warn!(context, "Cannot create MVBOX-folder {:?}: {}", folder, err);
             }
         }
-
         Ok(None)
     }