Summary:
Originally, the checksum of appended data in writable file writer is calculated after the data is copied to the buffer. It will not be able to catch the bit flip happens during copy. Move the checksum calculation before it.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6844
Test Plan: pass make asan_check
Reviewed By: cheng-chang
Differential Revision: D21576726
Pulled By: zhichao-cao
fbshipit-source-id: 0a062a1f19886f6ea0d4e3f557e6f4b799773254