problem formatting a line with heading spaces

Hi,
I encountered the following problem when trying to format a file
The file is

```
# a file with the problem
import sys

```

if I change the file to

```
# a file without the problem
import sys

```

The yapf works fine
(The only difference is the spacing before the import sys)

The following file also works fine

```
# a file without the problem
import sys

```

there is no .style.yapf in the folder (or it's ancestors)

The following is the yapf error

[problem_output.txt](https://github.com/google/yapf/files/2194627/problem_output.txt)