fix: Always use field.fieldname in preview_fields
fix: Always use field.fieldname in preview_fields

If building preview_fields from mandatory fields in get_preview_data, use the correct property "fieldname" instead of "name".
If not, subsequent db queries will fail with illegal column names.

StrellaGroup/frappe,mhbu50/frappe,adityahase/frappe,yashodhank/frappe,yashodhank/frappe,yashodhank/frappe,almeidapaulopt/frappe,adityahase/frappe,mhbu50/frappe,adityahase/frappe,almeidapaulopt/frappe,vjFaLk/frappe,saurabh6790/frappe,almeidapaulopt/frappe,almeidapaulopt/frappe,frappe/frappe,vjFaLk/frappe,saurabh6790/frappe,adityahase/frappe,mhbu50/frappe,StrellaGroup/frappe,frappe/frappe,mhbu50/frappe,saurabh6790/frappe,vjFaLk/frappe,StrellaGroup/frappe,yashodhank/frappe,saurabh6790/frappe,vjFaLk/frappe,frappe/frappe