add logging for failed synchronization
add logging for failed synchronization

Also eleminiate a user-side panic that slipped into production.

ChrisSchinnerl/Sia,MrStrong/Sia,mtlynch/Sia,mharkus/Sia,MrStrong/Sia,ericflo/Sia,mharkus/Sia,NebulousLabs/Sia,mtlynch/Sia,NebulousLabs/Sia,ChrisSchinnerl/Sia,ericflo/Sia