games/galaxyhack: Fix build with Clang 6
Group_Base.cpp:230:24: error: non-constant-expression cannot be narrowed from type 'int' to 'Sint16' (aka 'short') in initializer list [-Wc++11-narrowing]
SDL_Rect myRect = {static_cast<int>(myx), static_cast<int>(myy), width, height};
^~~~~~~~~~~~~~~~~~~~~... and more of these in various other files