fix: Tax withholding related fixes

(cherry picked from commit abf5b6be3e)

erpnext/accounts/doctype/tax_withholding_category/tax_withholding_category.py

@@ -419,7 +419,10 @@ def get_tds_amount(ldc, parties, inv, tax_details, tax_deducted, vouchers):
 		):
 			# Get net total again as TDS is calculated on net total
 			# Grand is used to just check for threshold breach
-			net_total = frappe.db.get_value("Purchase Invoice", invoice_filters, "sum(net_total)") or 0.0
+			net_total = 0
+			if vouchers:
+				net_total = frappe.db.get_value("Purchase Invoice", invoice_filters, "sum(net_total)")
+
 			net_total += inv.net_total
 			supp_credit_amt = net_total - cumulative_threshold