Add the missing hasFile() method to GenerateThumbnail

Author: dtdesign

wcfsetup/install/files/lib/event/file/GenerateThumbnail.class.php

@@ -23,6 +23,15 @@ public function __construct(
         public readonly ThumbnailFormat $thumbnailFormat,
     ) {}
 
+    /**
+     * Returns true if a file has already been set and no further files are
+     * being accepted.
+     */
+    public function hasFile(): bool
+    {
+        return isset($this->pathname);
+    }
+
     /**
      * Sets the pathname of the generated image unless it has already been set
      * in which case the call will throw an exception. You must check the result