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

Co-authored-by: rehanrehman389 <rehanrehman389@gmail.com>

Author: diptanilsaha

erpnext/accounts/doctype/journal_entry/journal_entry.py

@@ -180,7 +180,7 @@ 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):