Move png_image initialization into a function

rust/coffi/src/main.rs

@@ -19,6 +19,14 @@ struct png_image {
    message: [u8; 64],
}
impl png_image {
    fn new() -> png_image {
        let mut img: png_image = unsafe { std::mem::zeroed() };
        img.version = 1;
        return img
    }
}
impl std::fmt::Display for png_image {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        fn get_message(msg: [u8; 64]) -> String {
@@ -45,8 +53,7 @@ fn main() {
    println!("cos(3.1415) = {}", x);
    unsafe {
        let mut img: png_image = std::mem::zeroed();
        img.version = 1;
        let mut img = png_image::new();
        println!("{}", img);
        let res = png_image_begin_read_from_file(&mut img, "mei.png\0".as_ptr());
        println!("read_from_file: {}", res);