fixed assert when adding a torrent with resume data and immediately setting all piece priorities to 0
fixed assert when adding a torrent with resume data and immediately setting all piece priorities to 0

git-svn-id: 6ed3528c1be4534134272ad6dd050eeaa1f628d3@3417 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda

steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent