fix(Payment Entry): don't check empty references

Manual partial backport of https://github.com/frappe/erpnext/pull/36649

erpnext/accounts/doctype/payment_entry/payment_entry.py

@@ -175,6 +175,7 @@ class PaymentEntry(AccountsController):
 					frappe.throw(fail_message.format(d.idx))
 
 	def validate_allocated_amount_with_latest_data(self):
+		if self.references:
 			latest_references = get_outstanding_reference_documents(
 				{
 					"posting_date": self.posting_date,