Fixes bug in error reporting.

This should clarify some of the errors with encodings. Specifically the
'NoneType is not subscriptable' error preceded by an encoding error.

If this problem occurs, you will most likely fix it by by using a utf-8
ARFF file. These can be generated with WEKA as follows:

http://weka.wikispaces.com/Can+I+process+UTF-8+datasets+or+files%3F