Function stbi__check_png_header

lite/example/cpp_example/mge/cv/stb_image.h:4977–4984

}

static int stbi__check_png_header(stbi__context* s) {
    static const stbi_uc png_sig[8] = {137, 80, 78, 71, 13, 10, 26, 10};
    int i;
    for (i = 0; i < 8; ++i)
        if (stbi__get8(s) != png_sig[i])
            return stbi__err("bad png sig", "Not a PNG");
    return 1;
}

typedef struct {
    stbi__context* s;