didn't recognize QR codes, needs an error

[jesseaknight]

Short version:
if Zbar doesn't recognize any barcodes, sortphotos.py returns a cryptic error relating to line 146.
This case should be handled with an error message.

Background (in case my process is part of the problem)
I shot 250+ portraits last night after testing out your system and getting it working on my machine. Today I processed them all in Lightroom and exported them (IMG_0001_2.jpg is handled fine BTW).
The bardcodes filled the middle 1/3 of the frame and were originally 5616x3744, I'm guessing somewhere in the downsizing to 500x500 the code got too small to read. After some debugging, I cropped them and re-ran sortphotos.py and it worked.