[client-sync] fix unbouded query

Summary:
Fixes T7783

This unbounded query, plus a yet-to-be-diagnosed bug causing large numbers
of messages with no folderIds, led to frequent crashes of the worker
window at the end of every sync loop.

This took a fair amount to diagnose. Notes on that are here:
https://paper.dropbox.com/doc/Diagnosing-Crash-X329VTxevrqtIMESBtHNV

Huge thanks to @mark.

Test Plan: Reboot app with patch, no more crashes!

Reviewers: spang, halla, mark, juan

Reviewed By: mark, juan

Subscribers: mark

Maniphest Tasks: T7783

Differential Revision: https://phab.nylas.com/D4039

packages/client-sync/src/local-sync-worker/sync-worker.es6

@@ -101,6 +101,8 @@ class SyncWorker {
     const {Message, Thread, Folder, Label} = this._db;
 
     const messagesWithoutFolder = await Message.findAll({
+      attributes: ['id', 'threadId'],
+      limit: 1000,
       where: {
         folderId: null,
         isSent: {$not: true},
@@ -116,6 +118,8 @@ class SyncWorker {
     })
     .map(syncbackRequest => syncbackRequest.props.messageId)
     const messagesWithoutImapUID = await Message.findAll({
+      attributes: ['id', 'threadId'],
+      limit: 1000,
       where: {
         folderImapUID: null,
       },