title: get_fields is empty after inserting an ACF gutenberg block
body: <p>we just integrated timber into our acf-gutenberg-block setting, and we love it. ;)
  There is one thing that doesnt work.</p>
  <p>Our ACF Blocks have prefilled values like a &quot;dummy&quot; headline.
  But when a backend user adds a block into the gutenberg view, the get_fields() inside our render_callback function is empty. The user then changes the headline and then get_fields brings up all the fields and their values.</p>
  <p>any idea how to fix this problem on the first load of an acf block?</p>
  <p>the callback function looks like this (just like the one in the documentation)</p>
  <pre><code>function my_acf_block_render_callback($block, $content = '', $is_preview = false)
  {
      $context = Timber::context();
  
      // Store block values.
      $context['block'] = $block;
      // Store field values.
      $context['fields'] = get_fields();
      // Value for detecting editor-view in twig (like is admin())
      $context['is_preview'] = $is_preview;
  
      // Render the block.
      Timber::render('blocks/' . $block['template-name'] . '.html.twig', $context);
  }
  </code></pre>
  <p>cheers,</p>
  <p>ToM</p>