Fix bug in display of webp thumbs 2

diff --git a/src/library/media_jobs/WikiThumbDetailJob.php b/src/library/media_jobs/WikiThumbDetailJob.php
index d6b1d1ae9..aa91c7acc 100644
--- a/src/library/media_jobs/WikiThumbDetailJob.php
+++ b/src/library/media_jobs/WikiThumbDetailJob.php
@@ -166,7 +166,7 @@ class WikiThumbDetailJob extends MediaJob
                 || (C\nsdefined("IMAGE_MAGICK") && C\nsdefined("CALIBRE") &&
                 ($mime_type == 'application/epub+zip' ||
                 substr($mime_type, 0, 4) == 'text' ))) {
-                if (!file_exists("$thumb_folder/$name.jpg")) {
+                if (!file_exists("$thumb_folder/$name.webp")) {
                     $make_thumb = true;
                 }
                 if (!$make_thumb && $mime_parts[0] == 'video') {