add verifications before adding product

src/pages/add_product.tsx

@@ -20,7 +20,7 @@ const AddProduct = () => {
   }, []);
 
   function createItem() {
-    if (category_id !== "n/a") {
+    if (category_id !== "n/a" && name != "" && price > 0 && priceAdherant > 0 && stock > 0) {
       console.log("Creating item: " + name + " " + price + " " + priceAdherant + " " + stock + " " + category_id);
       addItem(name, price, priceAdherant, stock, category_id).then((data) => {
         console.log(data);