Bad error 'No such file or directory' when convert fails to run

[carolyncole]

When processing office categorized documents and the conversion to pdf fails you get a strange error message No Such file or directory instead of some indication that the pdf conversion failed.

This also shows as bad URI(is not URI?) when the original filename contains a space or other non URI character.

Here is where the conversion happens that is returning no output:
https://github.com/projecthydra/hydra-derivatives/blob/master/lib/hydra/derivatives/processors/document.rb#L38

It would be better to capture the error and or verify the file exists before passing on to the ImageProcessor: https://github.com/projecthydra/hydra-derivatives/blob/master/lib/hydra/derivatives/processors/document.rb#L24