Handle an empty file upload.
Handle an empty file upload.

If the sends no key file, catch the error (no file uploaded) and
redisplay the form with an error message.

tcmitchell/geni-portal,tcmitchell/geni-portal,charliemeyer/geni-portal,tcmitchell/geni-portal,charliemeyer/geni-portal,charliemeyer/geni-portal,tcmitchell/geni-portal,charliemeyer/geni-portal,tcmitchell/geni-portal,charliemeyer/geni-portal