guard against nil indentation values

This commit is intended to resolves an issue where the indentation
value can be nil (which leads to a run time exception)

This occurrs in cases where a section is following by only one of more
comments.

The proposed fix is to guard against potential nil values where the
error occurs. This fix is idential to code used at line 125 of the same file.
Merge pull request #30 from bodepd/fix_nil_indentation

guard against nil indentation values