Handle missing descr in Rabobank restructered files

Some files actually have no REMI token in the 86 record, and therefore
we end up with a NoMethodError for Nil-exception. So, if that is the
case, we simply set no description at all (there seems to be no sensible
alternative).
Merge pull request #2 from avdgaag/missing-descriptions

Handle missing descriptions in Rabobank restructered files