Closes the GzipFile object. Unlike Zlib::GzipFile#close, this method never
calls the close method of the
associated IO object. Returns the associated IO object.
static VALUE
rb_gzfile_finish(VALUE obj)
{
struct gzfile *gz = get_gzfile(obj);
VALUE io;
io = gz->io;
gzfile_close(gz, 0);
return io;
}