clang-format: Don't format unrelated nested blocks.

With this change:

  SomeFunction(
      [] {
	int i;
	 return i;  // Format this line.
      },
      [] {
	 return 2;  // Don't "fix" this.
      });

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@262216 91177308-0d34-0410-b5e6-96231b3b80d8