fix: Bulk update of valid upto field wasn't working (bp #28242)

* fix: Bulk update of valid upto field wasn't working

Check in dates for the price list was failing because valid_upto field was string. Converting to date fixed the problem.

* chore: extend fix and cleanup whitespace

Co-authored-by: Ankush Menat <ankush@frappe.io>
(cherry picked from commit 95a5ef1d416d54ecf0f557586b341b0dce2a0b05)

Co-authored-by: fatihustaoglu <46131068+fatihustaoglu@users.noreply.github.com>

erpnext/stock/doctype/item_price/item_price.py

@@ -6,6 +6,7 @@ from __future__ import unicode_literals
 import frappe
 from frappe import _
 from frappe.model.document import Document
+from frappe.utils import getdate
 
 
 class ItemPriceDuplicateItem(frappe.ValidationError):
@@ -27,7 +28,7 @@ class ItemPrice(Document):
 
 	def validate_dates(self):
 		if self.valid_from and self.valid_upto:
-			if self.valid_from > self.valid_upto:
+			if getdate(self.valid_from) > getdate(self.valid_upto):
 				frappe.throw(_("Valid From Date must be lesser than Valid Upto Date."))
 
 	def update_price_list_details(self):