Zero division error when uploading a file with zero GPS coordinates

[chrysn]

Files produced by a Nikon P510 have an odd GPS direction set, which makes mediagoblin/mediagoblin/tools/exif.py crash in line 180 (the gps_data['direction'] lambda -- denominator is zero).

As a result, the submission form shows a 503, the lazyserver console gives an appropriate backtrace and the file shows up as "failed" in the media processing panel.

This was tested with current master (763eae89d); if it helps, I can send an example picture by private EMail (don't have the camera at hand to create a blank example).

[ayleph]

I recently saw this on my own instance. I pushed a fix in ​07c535c and an additional unit test in ​66dbc22.