Do not close file after mmap (Windows version)

[dfyz]

This is the Windows version of #1017. Just as with Unix-based systems, closing the same handle twice is mostly harmless, but when working on #1010, I noticed that the duplicated CloseHandle() triggers an "Invalid handle" exception in the debugger:

(3f00.2cbc): Invalid handle - code c0000008 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
ntdll!KiRaiseUserExceptionDispatcher+0x3a:
00007ffb`5e072d6a 8b8424c0000000  mov     eax,dword ptr [rsp+0C0h] ss:0000008e`6cffd230=c0000008

You can skip this exception and continue debugging, but I think it's better to fix this properly.