Do not close file after mmap

[slaren]

Fixes #963

[prusnak]

There is no harm in not calling the close().

Since the underlying file is opened as read-only, the worst what can happen is that we will run out of file descriptors, which is hardly the case for llama.cpp.

Also, all file descriptors are closed by the kernel when the process exits.

[slaren]

The file should still be closed in the llama_file destructor, so I think this shouldn't cause any file descriptor leaks either.

[prusnak]

The file should still be closed in the llama_file destructor, so I think this shouldn't cause any file descriptor leaks either.

Right. I just confirmed that close() in ~llama_file() is called even when mmap() is used.