Fixed: error message when opening other user product

The user can only open their own products.
If the user tried to open a product that belongs to
other person, the site were returning an error message.

Now it just go back to the last page.

app/Http/Controllers/ProductController.php

@@ -62,10 +62,17 @@ class ProductController extends Controller
      * Show a specified Product
      * 
      * @param (int) $id The product id
+     * 
+     * @return \Illuminate\Http\Response
      */
     public function show($id)
     {
         $product = Product::fromAuthUser()->find($id);
+
+        if (!$product) {
+            return back();
+
+        }
         return view('product.show', compact('product'));
     }
 }