Some local messages missed in normalization: Refs #6604

Discovered earlier that it's possible for the folder normalization
to miss messages in the local store that have been removed from the
server at the upper end of the mail vector.  This solves that problem.

I noticed that with this fix, problem #6604 disappeared and the
conversation is now viewable.  It's possible this fixes that problem,
although I'm not sure how at this time.

src/engine/imap-engine/imap-engine-generic-folder.vala

@@ -135,13 +135,14 @@ private class Geary.ImapEngine.GenericFolder : Geary.AbstractFolder, Geary.Folde
         // fetch email from earliest email to last to (a) remove any deletions and (b) update
         // any flags that may have changed
         Geary.Imap.UID? earliest_uid = yield local_folder.get_earliest_uid_async(cancellable);
+        Geary.Imap.UID? latest_uid = yield local_folder.get_latest_uid_async(cancellable);
 
         // verify still open
         check_open("normalize_folders (local earliest UID)");
 
         // if no earliest UID, that means no messages in local store, so nothing to update
-        if (earliest_uid == null || !earliest_uid.is_valid()) {
-            debug("No earliest UID in local %s, nothing to normalize", to_string());
+        if (earliest_uid == null || !earliest_uid.is_valid() || latest_uid == null || !latest_uid.is_valid()) {
+            debug("No earliest and/or latest UID in local %s, nothing to normalize", to_string());
 
             return true;
         }
@@ -361,9 +362,10 @@ private class Geary.ImapEngine.GenericFolder : Geary.AbstractFolder, Geary.Folde
             current_start_id = new Geary.Imap.EmailIdentifier(current_end_id.uid.next(),
                 current_start_id.folder_path);
 
-            // TODO: If UIDNEXT isn't available, will need to fetch the highest UID from the server
-            // and the highest ID from the local store
-            if (current_start_id.uid.compare(remote_properties.uid_next) >= 0)
+            // if gone past both local and remote extremes, time to exit
+            // TODO: If UIDNEXT isn't available on server, will need to fetch the highest UID
+            if (current_start_id.uid.compare(latest_uid) >= 0
+                && current_start_id.uid.compare(remote_properties.uid_next) >= 0)
                 break;
         }