fix: ignore if df doesn't exist (#18358) (#18360)

(cherry picked from commit b03e0752b9)

Co-authored-by: Ankush Menat <ankush@frappe.io>

frappe/public/js/frappe/ui/field_group.js

@@ -169,6 +169,9 @@ frappe.ui.FieldGroup = class FieldGroup extends frappe.ui.form.Layout {
 	}
 
 	set_df_property(fieldname, prop, value) {
+		if (!fieldname) {
+			return;
+		}
 		const field = this.get_field(fieldname);
 		field.df[prop] = value;
 		field.refresh();