Correctly handle an empty spiderlist

see 96dced2d6197d64f30b6638f3966a8778c586cd6

diff --git a/wcfsetup/install/files/lib/system/cache/builder/SpiderCacheBuilder.class.php b/wcfsetup/install/files/lib/system/cache/builder/SpiderCacheBuilder.class.php
index 7e94ca3d35f3a904aaec97ccc6cd718e92176a46..9440c938d70d4889d45bead94c7102716cb36217 100644 (file)
--- a/wcfsetup/install/files/lib/system/cache/builder/SpiderCacheBuilder.class.php
+++ b/wcfsetup/install/files/lib/system/cache/builder/SpiderCacheBuilder.class.php
@@ -49,6 +49,11 @@ class SpiderCacheBuilder extends AbstractCacheBuilder
                 );
             }
 
+            if ($regex === '') {
+                // This regex will never match anything.
+                $regex = '(?!)';
+            }
+
             return [
                 'regex' => "/{$regex}/",
                 'mapping' => $mapping,