MFH: r432973 r432974

games/frobtads, games/qtads: unbreak with clang 4.0

tads3/vmtz.cpp:1987:30: error: ordered comparison between pointer and zero ('vmtz_trans *' and 'int')

result->set(tcur > 0 ? tcur - 1 : tcur);
            ~~~~ ^ ~

PR: 216357
Reported by: antoine (via exp-run)
Submitted by: kaiwang27@gmail.com (maintainer)
Approved by: ports-secteam blanket