fix update stock

src/pages/stock.tsx

@@ -8,7 +8,7 @@ const Stock = () => {
   let [search, setSearch] = useState("");
   let [productsList, setProductsList] = useState<Product[]>([]);
   let [rawProductList, setRawProductList] = useState<Product[]>([]);
-  let oldQuantity = 0;
+  let [oldQuantity, setOldQuantity] = useState((0));
   
   useEffect(() => {
     // Filter products by name with the search term
@@ -48,7 +48,7 @@ const Stock = () => {
         console.log("error update stock BACK");
       });
     }else{
-      oldQuantity = product.stock;
+      setOldQuantity(product.stock);
     }
   };