Fix conversion from fieldValues to account field
Fix conversion from fieldValues to account field

When fieldValues was an empty object it was considered as a valid account.

cozy-labs/konnectors,clochix/konnectors,nicofrand/konnectors,m4dz/konnectors,poupotte/konnectors,cozy-labs/konnectors,poupotte/konnectors,frankrousseau/konnectors,clochix/konnectors,nicofrand/konnectors,m4dz/konnectors,nono/konnectors,nono/konnectors,poupotte/konnectors,cozy-labs/konnectors,m4dz/konnectors,nicofrand/konnectors,nono/konnectors,frankrousseau/konnectors,frankrousseau/konnectors,clochix/konnectors