Should sqlconfig processing be hardened to presume the file contents may have been logically corrupted

[stuartpa]

Right now sqlcmd presumes the sqlconfig file has been only edited by sqlcmd (or code using what will be the go-sqlcmd/sqlconfig package).

Of course a human may go into the sqlconfig file on disk and edit its contents. This would lead to panics in sqlcmd, as sqlcmd hasn't been hardened to this.