Buglet in new QR code functionality

[nneul]

Not a full bug report, just passing along a mini one since I tried it out after nerding out over your commit message when I pulled latest.

Describe the bug

Invalid (non parsable but looks like a qr code) resulting image and no error report complaining about the data being invalid/wrong format/etc.:

data qrcode -d https://some.url.com

Yes, I know that isn't valid based on reading the usage afterwards, who RTFM's before trying stuff at random? :)

Seg fault:
data qrcode -d aa

[nneul]

Works fine with multiple hex bytes. (i.e. not giving garbage input) - but the single byte segfault was unexpected.