tests/test-pull-http.out

bookmarks: Only save undo.bookmarks if bookmarks exist

Otherwise the command will abort when there is no .hg/bookmarks file.

adding a
updating working directory
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% expect error, cloning not allowed
abort: error: 
requesting all changes
% serve errors
% expect error, pulling not allowed
abort: error: 
pulling from http://localhost/
searching for changes
% serve errors