title: Product get_sale_price is always 0 when using Discount Rules for WooCommerce plugin
body: <p>This is my WordPress configuration (Just upgraded everything, so everything is up to date):<br>
  WordPress: 5.4<br>
  WooCommerce: 4.0.1<br>
  <a href="https://wordpress.org/plugins/woo-discount-rules/" rel="nofollow noreferrer">Discount Rules for WooCommerce</a>: 1.9.7  </p>
  
  <p>Discount Rules for WooCommerce configuration, per quantity block:<br>
  1-4 : 10%<br>
  5-24: 20%<br>
  25-99999: 30%  </p>
  
  <p>This is working perfectly fine on the shop and shop can even get orders properly with discounts.
  The thing is that I want to remove SALE! badge from the products as it is automatically added because of 1-4 quantity block which means default 10% site-wide discount as per the configuration.</p>
  
  <p>Now, here is my code in theme's functions.php</p>
  
  <pre><code>function wc_custom_replace_sale_text($html, $post, $product) {
    if ($product-&gt;is_on_sale()) {
      $regular_price = $product-&gt;get_regular_price();
      $sale_price = $product-&gt;get_sale_price();
      return '&lt;span class="onsale force-display"&gt;' . $sale_price . '&lt;/span&gt;';
    }
  }
  add_filter( 'woocommerce_sale_flash', 'wc_custom_replace_sale_text', 10, 3 );
  </code></pre>
  
  <p><strong>Problem</strong>: No matter what I try, I always get <code>$product-&gt;get_sale_price()</code> result always 0. And, the strange thing is that <code>$product_is_on_sale()</code> result is <code>true</code>.</p>
  
  <p>Because of this I cannot find out the product discount and so cannot remove SALE label for the 1-4 quantity block.</p>