Fail harder when saving message data fails.
Fail harder when saving message data fails.

This should abort the whole initial sync, since who knows what's going
on---programming error, S3 API is down, whatever. We may want to be
smarter about dealing with S3-related network errors in the future, but
for now let's err on the side of being conservative.

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