-Changed the block line iterator to skip over the first entry in a block's list of linedefs if co_blockmapfix is enabled. This first entry appears to have had a special purpose during vanilla Doom's development but was removed before release and so the first entry contains garbage, most often referencing linedef 0. In effect, linedef 0 is included in every block, causing hitscan collision issues under the right circumstances.

git-svn-id: http://odamex.net/svn/root/trunk@3859 b0bcef46-2027-0410-bd56-ab726e9a1d04