[client-sync] Make imap ended error retryable
[client-sync] Make imap ended error retryable

Summary: This error should really be retryable, and will prevent more red boxes

Test Plan: manual

Reviewers: evan, spang

Reviewed By: evan, spang

Differential Revision: https://phab.nylas.com/D3982

simonft/nylas-mail,nylas-mail-lives/nylas-mail,nylas/nylas-mail,nirmit/nylas-mail,nylas/nylas-mail,nirmit/nylas-mail,nylas-mail-lives/nylas-mail,nylas/nylas-mail,nylas/nylas-mail,simonft/nylas-mail,nirmit/nylas-mail,simonft/nylas-mail,nirmit/nylas-mail,nirmit/nylas-mail,nylas-mail-lives/nylas-mail,nylas/nylas-mail,nylas-mail-lives/nylas-mail,simonft/nylas-mail,simonft/nylas-mail,nylas-mail-lives/nylas-mail