Remove assertion when syncing back drafts.
Remove assertion when syncing back drafts.

We can occasionally try to sync back a draft that isn't actually a draft
anymore. This isn't really a problem, so just return instead of throwing an
AssertionError.

EthanBlackburn/sync-engine,closeio/nylas,Eagles2F/sync-engine,closeio/nylas,ErinCall/sync-engine,PriviPK/privipk-sync-engine,EthanBlackburn/sync-engine,jobscore/sync-engine,EthanBlackburn/sync-engine,nylas/sync-engine,ErinCall/sync-engine,Eagles2F/sync-engine,wakermahmud/sync-engine,EthanBlackburn/sync-engine,EthanBlackburn/sync-engine,jobscore/sync-engine,ErinCall/sync-engine,Eagles2F/sync-engine,Eagles2F/sync-engine,gale320/sync-engine,gale320/sync-engine,wakermahmud/sync-engine,PriviPK/privipk-sync-engine,wakermahmud/sync-engine,closeio/nylas,gale320/sync-engine,closeio/nylas,PriviPK/privipk-sync-engine,ErinCall/sync-engine,jobscore/sync-engine,Eagles2F/sync-engine,wakermahmud/sync-engine,jobscore/sync-engine,gale320/sync-engine,nylas/sync-engine,ErinCall/sync-engine,nylas/sync-engine,PriviPK/privipk-sync-engine,gale320/sync-engine,wakermahmud/sync-engine,PriviPK/privipk-sync-engine,nylas/sync-engine