Fix Windows server history scrolling

Update history position when CON_HistNext goes to input line, otherwise
when going to previous a line is skipped.
Don't let CON_HistPrev go to unused lines.
Add assignment below declarations otherwise compiling fails with msvc

Signed-off-by: Zack Middleton <zturtleman@gmail.com>
Merge remote-tracking branch 'ioquake3/master'