Indicate that nothing was found in the docs when searching

refs #8847

modules/doc/application/views/scripts/search/index.phtml

@@ -1,8 +1,8 @@
 <div class="content">
     <?php foreach (/** @var \Icinga\Module\Doc\Renderer\DocSearchRenderer[] $searches */ $searches as $title => $search): ?>
-        <?php if (! $search->isEmpty()): ?>
-            <h1><?= $this->escape($title) ?></h1>
-            <?= $search ?>
-        <?php endif ?>
+        <h1><?= $this->escape($title) ?></h1>
+        <?= $search->isEmpty()
+            ? $this->translate('No documentation found matching the filter')
+            : $search ?>
     <?php endforeach ?>
 </div>