Explicit netcdf dumper error message when trying to append to non-existant file

[prs513rosewood]

Summary

Previous behavior would print "at keyword requires use of 'append yes'" when trying to append to non-existant file, which was confusing. It now prints "cannot append to a non-existant file filename".

Author(s)

Lucas Frérot, Department of Physics and Astronomy, Johns Hopkins University

Licensing

By submitting this pull request, I agree, that my contribution will be included in LAMMPS and redistributed under either the GNU General Public License version 2 (GPL v2) or the GNU Lesser General Public License version 2.1 (LGPL v2.1).

Backward Compatibility

Should be ok.

Implementation Notes

I make use of utils::file_is_readable instead of access(2) from unistd.h, and use of fmt::format to print the filename.

Post Submission Checklist

• The feature or features in this pull request is complete
• Licensing information is complete
• Corresponding author information is complete
• The source code follows the LAMMPS formatting guidelines
• Suitable new documentation files and/or updates to the existing docs are included
• The added/updated documentation is integrated and tested with the documentation build system
• The feature has been verified to work with the conventional build system
• The feature has been verified to work with the CMake based build system
• Suitable tests have been added to the unittest tree.
• A package specific README file has been included or updated
• One or more example input decks are included

Further Information, Files, and Links

[akohlmey]

@prs513rosewood thanks for the change. This looks nice. Getting rid of "unistd.h" is a good thing as will improve portability.