fix: dont db_set on unsaved document (#18460)

(cherry picked from commit 1bd61d5)

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

frappe/model/document.py

@@ -1169,6 +1169,9 @@ def db_set(self, fieldname, value=None, update_modified=True, notify=False, comm
 		# to trigger notification on value change
 		self.run_method("before_change")
 
+		if self.name is None:
+			return
+
 		frappe.db.set_value(
 			self.doctype,
 			self.name,