clang-format: Don't confuse operator[] with lambdas.

Before:
  double &operator[](int i) { return 0; } int i;

After:
  double &operator[](int i) { return 0; }
  int i;

This fixes llvm.org/PR17134.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190207 91177308-0d34-0410-b5e6-96231b3b80d8