EBookBackendFile: Reduce uneeded warnings in server logs
EBookBackendFile: Reduce uneeded warnings in server logs

With this patch, only unknown errors, which the user is not expected
to handle or recover from (such as internal SQLite errors or file system
errors), are warned about in the stderr.

tintou/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,matzipan/evolution-data-server,tintou/evolution-data-server,tintou/evolution-data-server