server: Set the fd user when duplicating a mapping file descriptor into a new file.
diff --git a/server/file.c b/server/file.c
index fe88495..fcfd572 100644
--- a/server/file.c
+++ b/server/file.c
@@ -162,6 +162,7 @@
             release_object( file );
             return NULL;
         }
+        set_fd_user( file->fd, &file_fd_ops, &file->obj );
     }
     return file;
 }