Fix issue #14 that a binary value renders invalid SQL.

[mvoppen]

This fix do not address the question why a binary value is created for 'Y' in but not in .
Nevertheless the fix at this position basically is a check for an invalid return value, makes the code more stable and fixes the issue.

[dataflake]

@igs165 Have you signed either the Zope Foundation contributor agreement or the new Plone Foundation agreement? It doesn't look like it. Please see https://www.zope.org/developer/becoming-a-committer.html and finish that process before anyone here can merge your contribution.

[mvoppen]

I've filed the Contributer agreement to agreements@plone.org now. That was not so easy as agreements@plone.org aka Google Groups rejected all emails as Spam. Maybe I should open an issue that plone.org should search for a more serious and reputable email provider.

[dataflake]

I'll look at this either tonight or tomorrow. I want to remove the note next to the change because that's what a change log entry is for.

[dataflake]

Fixed in b18e316

Going forward, please create branched right in here and not off in your own private fork. Makes it so much easier for people to collaborate on the branch.