Fix KeyError in Gmail mailsync's add_new_imapuids()
Fix KeyError in Gmail mailsync's add_new_imapuids()

Messages can still move around while a given IMAP session is open, so
sometimes we'll start adding ImapUid entries but not get the flag info
while the message is still in the given folder. (For example, when a
message is archived in the middle of this operation.)

The right thing to do in this situation is to skip adding the ImapUid
entry; we'll catch the message later via the All Mail sync.

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