fix(postgres): get_item_price picks undated price on Postgres

Both Item Price lookups order by valid_from desc and take the first valid row.
MariaDB sorts NULL valid_from last; Postgres first, so the undated base price was
winning over a dated one. Order by (valid_from IS NULL) asc, valid_from desc (the
get_all is converted to qb since its order_by won't take such an expression).
MariaDB output is unchanged.

erpnext/stock/get_item_details.py

@@ -1121,17 +1121,20 @@ def insert_item_price(ctx: ItemDetailsCtx):
 		or getdate()
 	)
 
-	item_prices = frappe.get_all(
+	ip = frappe.qb.DocType("Item Price")
-		"Item Price",
+	item_prices = (
-		filters={
+		frappe.qb.from_(ip)
-			"item_code": ctx.item_code,
+		.select(ip.name, ip.price_list_rate, ip.valid_from, ip.valid_upto)
-			"price_list": ctx.price_list,
+		.where(
-			"currency": ctx.currency,
+			(ip.item_code == ctx.item_code)
-			"uom": ctx.stock_uom,
+			& (ip.price_list == ctx.price_list)
-		},
+			& (ip.currency == ctx.currency)
-		fields=["name", "price_list_rate", "valid_from", "valid_upto"],
+			& (ip.uom == ctx.stock_uom)
-		order_by="valid_from desc, creation desc",
+		)
-	)
+		.orderby(ip.valid_from.isnull(), order=frappe.qb.asc)
+		.orderby(ip.valid_from, order=frappe.qb.desc)
+		.orderby(ip.creation, order=frappe.qb.desc)
+	).run(as_dict=True)
 	item_price = next(
 		(
 			row
@@ -1233,6 +1236,7 @@ def get_item_price(
 			& (ip.price_list == pctx.price_list)
 			& (IfNull(ip.uom, "").isin(["", pctx.uom]))
 		)
+		.orderby(ip.valid_from.isnull(), order=frappe.qb.asc)
 		.orderby(ip.valid_from, order=frappe.qb.desc)
 		.orderby(IfNull(ip.batch_no, ""), order=frappe.qb.desc)
 		.orderby(ip.uom, order=frappe.qb.desc)