don't fall back on wildcard port in UPnP

git-svn-id: http://libtorrent.googlecode.com/svn@10001 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda
merged UPnP fix from RC_0_16

git-svn-id: http://libtorrent.googlecode.com/svn@10002 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda