fix(stock): guard traceability qty division against a zero divisor (Postgres)

get_materials divides stock_entry_detail.qty by a CASE that returns
fg_completed_qty when it is > 0 and otherwise the injected sabb_data.qty. The
code explicitly anticipates fg_completed_qty <= 0 (the else branch), and
neither fg_completed_qty nor sabb_data.qty is constrained non-zero, so the
divisor can be 0. MariaDB returns NULL for x/0; PostgreSQL raises
`division by zero` and aborts the report. Wrapping the CASE in NullIf(..., 0)
makes the divisor NULL instead of 0 — unchanged on MariaDB, valid on Postgres.

erpnext/stock/report/serial_no_and_batch_traceability/serial_no_and_batch_traceability.py

@@ -4,6 +4,7 @@
 import frappe
 from frappe import _
 from frappe.query_builder import Case
+from frappe.query_builder.functions import NullIf
 
 
 def execute(filters: dict | None = None):
@@ -300,9 +301,12 @@ class ReportData:
 				(
 					(
 						stock_entry_detail.qty
-						/ Case()
-						.when(stock_entry.fg_completed_qty > 0, stock_entry.fg_completed_qty)
-						.else_(sabb_data.qty)
+						/ NullIf(
+							Case()
+							.when(stock_entry.fg_completed_qty > 0, stock_entry.fg_completed_qty)
+							.else_(sabb_data.qty),
+							0,
+						)
 					)
 					* sabb_data.qty
 				).as_("qty"),