devel/kyra: Fix build with Clang 6

engine.cpp:454:27: error: non-constant-expression cannot be narrowed from type 'int' to 'Sint16' (aka 'short') in initializer list [-Wc++11-narrowing]

SDL_Rect sdlrect = { rect.min.x, rect.min.y, rect.Width(), rect.Height() };
                     ^~~~~~~~~~

http://beefy11.nyi.freebsd.org/data/head-i386-default/p477696_s338122/logs/errors/kyra-2.1.3_4.log