clang-format: Fix indentation corner case.

Before:
  aaaaaaaaaa(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa)
                 .aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa);
  aaaaaaaaaa = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa)
                   .aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa();

After:
  aaaaaaaaaa(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
                 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa)
                 .aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa);
  aaaaaaaaaa = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa)
                   .aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa();

Probably still not ideal, but should be a step into the right direction.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@197557 91177308-0d34-0410-b5e6-96231b3b80d8