fix compilation errors for which i32->u32
fix compilation errors for which i32->u32

Rust-SDL2/rust-sdl2,Cobrand/rust-sdl2,Rust-SDL2/rust-sdl2,Rust-SDL2/rust-sdl2,Cobrand/rust-sdl2,AngryLawyer/rust-sdl2,Cobrand/rust-sdl2