Segmentation fault on empty string

[chifung7]

PDF417.new(text: '').to_blob would segfault. A simple fix may be just rasing error on empty string. I also look at other 2d barcode. It seems that QR Code is able to encode empty string. Not sure how PDF417 should handle this corner case.

[jamesprior]

Segfaulting tells me that it is something in the C module that is causing a problem. It would be nice I think to fix that, but I also don't see a solid case for needing an empty barcode. An easier fix would be to peek into the the Ruby wrapper and just not invoke the PDF417::Lib portion if the text to be encoded is empty.

It may be a while before I get to fixing that, is it something you'd be interested in submitting as an MR? Maybe just raise an exception with a helpful error in PDF417#generate?

[jamesprior]

So in trying to test #8 I was able to reproduce this on 2.1.9p490 and I think I've got a fix in master now. If you don't mind, could you please pull and re-test? I've tested with ruby 2.1.9p490 and ruby 2.2.5p319

If it looks like it's working for you now I'll push a release.