[v1.0.0] Mmap fails on empty files

[lmichaelis]

    Hit runtime exception, at loading "Chronicles of Myrtana" mod:

...\TheChroniclesOfMyrtana\_work\Data\Scripts\_compiled\Fight.dat - is empty file, that causes mmap to fail internally.

// _deps\mio-src\include\mio\detail\mmap.ipp
inline mmap_context memory_map(const file_handle_type file_handle, const int64_t offset,
    const int64_t length, const access_mode mode, std::error_code& error)
{
...
    char* mapping_start = static_cast<char*>(::MapViewOfFile(
            file_mapping_handle,
            mode == access_mode::read ? FILE_MAP_READ : FILE_MAP_WRITE,
            win::int64_high(aligned_offset),
            win::int64_low(aligned_offset),
            length_to_map));
    if(mapping_start == nullptr) // <-- file exists, but mapping is null
    {
...

Originally posted by @Try in https://github.com/Try/OpenGothic/issues/271#issuecomment-1301469337

[lmichaelis]

This seems to be a problem with MapViewOfFile rather than mio. If it returns nullptr if the file is empty, then mio can't do anything about that. Regardless of that, any read from that file would fail anyways so the caller has to deal with the error.