stb_image: fix CRC reading at the end of IEND chunk in png file

[Try]

The problem

stb consistently under reads last 4 bytes of *png file.

Why this happends

in function stbi__parse_png_file we have a code:

static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
{
...
   for (;;) {
      stbi__pngchunk c = stbi__get_chunk_header(s);
      switch(c.type) {
        ...
        case STBI__PNG_TYPE('I','E','N','D'): {
            ...
            return 1; // <--- CRC-read, will be skipped because of this 'return'
        }
      }
      ...
      stbi__get32be(s); // for normal chunk stb reading CRC here
   }
}

Why this is a problem

In my video-game I have a screen-shoot inside save-file binary:

[ header ][ png-priview ][ data ]

And to make it work I need a byte-exact png-reader/writer.

[nothings]

Makes sense.