Those empty spans are needed for the inline editing on the website (you can click there and add text directly.
Use printAlbumDesc(false,'',false)
Always a good idea to look at the docs:
http://www.zenphoto.org/documentation/functions/_template-functions.php.html#functionprintAlbumDesc
Of course something like if(getAlbumDesc() != "") { echo getAlbumDesc(); } would work, too.
@barbara
I used the example acrylian did on my last theme. I only used it deciding if I needed to add captioning to a lightbox though. As acrylian said, if you don't have it on your image page you won't be able to edit it from there while logged in as admin. Remember that your gallery views are different when you're logged in than when a normal users views your site.