If CSV v2 format is in use and an invalid field is specified in the header (eg EmailAddress.mail instead of EmailAddress.mail.personal), a full sync job appears to fail abruptly, leaving a Job "In Progress" (even if it's no longer running) and a stale lock. FileSource should instead fail gracefully with an error message.

(Note the scope of this ticket is not to update JobShell to never leave a stale lock, it is to add better error detection to FileSource.)