Issue #3460605 by jesss: footnotes.css not loaded when both Use footnotes CSS and Open footnote references in a dialog options are selected

Closes #3460605

src/Plugin/Filter/FootnotesFilter.php

@@ -182,7 +182,7 @@ class FootnotesFilter extends FilterBase implements ContainerFactoryPluginInterf
 
     // Only use CSS if option is selected.
     if (!isset($this->settings['footnotes_css']) || $this->settings['footnotes_css']) {
-      $result->setAttachments([
+      $result->addAttachments([
         'library' => [
           'footnotes/footnotes',
         ],
@@ -191,7 +191,7 @@ class FootnotesFilter extends FilterBase implements ContainerFactoryPluginInterf
 
     // Only use dialog if option is select.
     if (isset($this->settings['footnotes_dialog']) && $this->settings['footnotes_dialog']) {
-      $result->setAttachments([
+      $result->addAttachments([
         'library' => [
           'footnotes/footnotes.dialog',
         ],