Fix bug in display of webp thumbs 5

diff --git a/src/controllers/ResourceController.php b/src/controllers/ResourceController.php
index 553e31edd..d2466641d 100644
--- a/src/controllers/ResourceController.php
+++ b/src/controllers/ResourceController.php
@@ -169,7 +169,6 @@ class ResourceController extends Controller implements CrawlConstants
                 }
             }
         }
-        $alt_path = $path;
         if (substr($path, -4) == 'webp') {
             $alt_path = substr($path, 0, -4) . "jpg";
             if (!file_exists($path) && file_exists($alt_path)) {