Fix ClangTidyOptions constructor to initialize all members. Fixes bug introduced in r207652.

Reviewers: rsmith

Subscribers: cfe-commits, alexfh, klimek

Differential Revision: http://reviews.llvm.org/D3578

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@207715 91177308-0d34-0410-b5e6-96231b3b80d8