vt: fix some signed/unsigned comparison problems
vt: fix some signed/unsigned comparison problems

Signed-off-by: Marc Andre Tanner <cc7c5be316e48d137cbb549833b85d91034d799d@brain-dump.org>

delphinus35/dvtm,benjohnson2001/dvtm,tgvaughan/dvtm,benjohnson2001/dvtm,medgar123/dvtm,gridsystem/dvtmx,medgar123/dvtm,seanyeh/dvtm,lotrfan/dvtm,tgvaughan/dvtm,gridsystem/dvtmx,seanyeh/dvtm,raedwulf/dvtm,lotrfan/dvtm,armanbilge/dvtm,benjohnson2001/dvtm,armanbilge/dvtm,tgvaughan/dvtm,seanyeh/dvtm,raedwulf/dvtm,lotrfan/dvtm,raedwulf/dvtm,medgar123/dvtm,delphinus35/dvtm