Potential feature: Add error handling for missing files

I had the issue that this action completes successfully even if some (or all) of the files specified to be zipped are missing. This seems like it may be desirable in some cases, but I'd guess that in most cases aborting the pipeline if files are missing would be more desirable.

In any case, I think it'd be nice to have an option to specify that you'd like an error thrown if files are missing 🙂 