fix: ensure SellingController.onload gets called for SO & DN

(cherry picked from commit 8431e3c275)

erpnext/stock/doctype/delivery_note/delivery_note.py

@@ -208,6 +208,8 @@ class DeliveryNote(SellingController):
 			)
 
 	def onload(self):
+		super().onload()
+
 		if self.docstatus == 0:
 			self.set_onload("has_unpacked_items", self.has_unpacked_items())