test_win_keygrab: Fix buffer not null terminated error.
test_win_keygrab: Fix buffer not null terminated error.

This fixes coverity CID 1308264.

FlorentRevest/Elementary,rvandegrift/elementary,tasn/elementary,rvandegrift/elementary,rvandegrift/elementary,FlorentRevest/Elementary,FlorentRevest/Elementary,tasn/elementary,FlorentRevest/Elementary,tasn/elementary,rvandegrift/elementary,tasn/elementary,tasn/elementary