T131820752 solve potential memleak in OnDiskInvertedLists::do_mmap (#2471)
T131820752 solve potential memleak in OnDiskInvertedLists::do_mmap (#2471)

Summary:
prevents resource leak in function OnDiskInvertedLists::do_mmap as the file is not closed when mmap fails.
solve [issue 2427](https://github.com/facebookresearch/faiss/issues/2427)

Pull Request resolved: https://github.com/facebookresearch/faiss/pull/2471

Test Plan:
cd build
make -j
make test

Reviewed By: mdouze

Differential Revision: D39539304

Pulled By: AbdelrahmanElmeniawy

fbshipit-source-id: 07985c5a4fc67facb67221d317c0978a4278464d

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