clang-format: Fix selective indentaiton in nested blocks.

Buggy case:
  someFunction(
      [] {
        // comment
        int i; // invoke formatting here.
      },       // force line break
      aaa);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@236091 91177308-0d34-0410-b5e6-96231b3b80d8