fix a small error with PDF417 encoding and a margin of zero
fix a small error with PDF417 encoding and a margin of zero

git-tfs-id: [https://tfs.codeplex.com/tfs/TFS05/]$/ZXingNet/trunk;C86963

DHMechatronicAG/ZXing.Net,bsoja/ZXing.Net,bsoja/ZXing.Net,micjahn/ZXing.Net,micjahn/ZXing.Net,DHMechatronicAG/ZXing.Net,bsoja/ZXing.Net,DHMechatronicAG/ZXing.Net,micjahn/ZXing.Net