[fix] validate preferred email if set in employee.py
[fix] validate preferred email if set in employee.py

geekroot/erpnext,geekroot/erpnext,gsnbng/erpnext,geekroot/erpnext,indictranstech/erpnext,indictranstech/erpnext,gsnbng/erpnext,gsnbng/erpnext,gsnbng/erpnext,Aptitudetech/ERPNext,geekroot/erpnext,indictranstech/erpnext,indictranstech/erpnext