Avoid saving product data if nothing was returned (#101)

* fix: Check if productData is set first

Throughout my testing and debugging, it was possible for productData to
be "undefined". To prevent errors, it's best to check for it's existence
first.

Signed-off-by: Colton Wolkins (Laptop) <colton@indicio.tech>

* fix: avoid saving wishlist when there's no change

Signed-off-by: Colton Wolkins (Laptop) <colton@indicio.tech>

---------

Signed-off-by: Colton Wolkins (Laptop) <colton@indicio.tech>

src/structures/Wishlist.js

@@ -161,6 +161,8 @@ class Wishlist {
     }
 
     const productData = await getProductData(item.url)
+    if (!productData) return; // short-circuit when there's no data
+
     for (const key of ['name', 'price', 'image']) {
       if (productData[key]) item[key] = productData[key]
     }