Fix clang-tidy script (#25652)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25652
The clang-tidy driver script generates a chunk whitelist per file so
that it only shows errors for lines that were actually changed. If a
change removes the chunk the count is equal to 0. If the chunk happens
to be at the start of the file, and the start position is equal 0,
clang-tidy fails to run. This change filters out those chunks.
Test Plan: Imported from OSS
Differential Revision: D17184188
Pulled By: pietern
fbshipit-source-id: b6c2d9dca4d52cd6bf4b186603545312726fb00b
