chore(stock_ledger): drop redundant check

Commit c2d7461d3cac639778e7740c4b08e459332a6b14 dropped a usage of
`last_valuation_rate` around this code block. After that, it was always checked
although the value would be None as it was being explicitly set above.

Signed-off-by: Akhil Narang <me@akhilnarang.dev>
diff --git a/erpnext/stock/stock_ledger.py b/erpnext/stock/stock_ledger.py
index db71fe2..d3807b0 100644
--- a/erpnext/stock/stock_ledger.py
+++ b/erpnext/stock/stock_ledger.py
@@ -1464,8 +1464,6 @@
 	if not company:
 		company = frappe.get_cached_value("Warehouse", warehouse, "company")
 
-	last_valuation_rate = None
-
 	# Get moving average rate of a specific batch number
 	if warehouse and serial_and_batch_bundle:
 		batch_obj = BatchNoValuation(
@@ -1482,21 +1480,18 @@
 		return batch_obj.get_incoming_rate()
 
 	# Get valuation rate from last sle for the same item and warehouse
-	if not last_valuation_rate or last_valuation_rate[0][0] is None:
-		last_valuation_rate = frappe.db.sql(
-			"""select valuation_rate
-			from `tabStock Ledger Entry` force index (item_warehouse)
-			where
-				item_code = %s
-				AND warehouse = %s
-				AND valuation_rate >= 0
-				AND is_cancelled = 0
-				AND NOT (voucher_no = %s AND voucher_type = %s)
-			order by posting_date desc, posting_time desc, name desc limit 1""",
-			(item_code, warehouse, voucher_no, voucher_type),
-		)
-
-	if last_valuation_rate:
+	if last_valuation_rate := frappe.db.sql(
+		"""select valuation_rate
+		from `tabStock Ledger Entry` force index (item_warehouse)
+		where
+			item_code = %s
+			AND warehouse = %s
+			AND valuation_rate >= 0
+			AND is_cancelled = 0
+			AND NOT (voucher_no = %s AND voucher_type = %s)
+		order by posting_date desc, posting_time desc, name desc limit 1""",
+		(item_code, warehouse, voucher_no, voucher_type),
+	):
 		return flt(last_valuation_rate[0][0])
 
 	# If negative stock allowed, and item delivered without any incoming entry,