Filter on account.sync_should_run in syncback worker.
Filter on account.sync_should_run in syncback worker.

This lets the query use the compound index on
`(account.sync_should_run, account.sync_host)`.

nylas/sync-engine,closeio/nylas,nylas/sync-engine,closeio/nylas,nylas/sync-engine,jobscore/sync-engine,closeio/nylas,closeio/nylas,jobscore/sync-engine,jobscore/sync-engine,nylas/sync-engine,jobscore/sync-engine