fix: preserve custom title on new JV (backport #57987) (#57989)

Co-authored-by: Diptanil Saha <diptanil@frappe.io>
Co-authored-by: rehanrehman389 <rehanrehman389@gmail.com>

Author: 3 people

erpnext/accounts/doctype/journal_entry/journal_entry.py

@@ -162,7 +162,7 @@ def validate(self):
 
 		JournalTaxWithholding(self).on_validate()
 
-		if self.is_new() or not self.title:
+		if not self.title or (self.is_new() and self.amended_from):
 			self.title = self.get_title()
 
 	def validate_advance_accounts(self):