Improve error message when filename does not exist
When listing a filename
in input_files
pointing to a file which does not exist, we get an error message like this:
Use of uninitialized value $fname in -f at rbm/lib/RBM.pm line 745.
Use of uninitialized value $fname in -l at rbm/lib/RBM.pm line 746.
Error: Template Error:
undef error - Path::Tiny paths require defined, positive-length parts at rbm/lib/RBM.pm line 747.
We should instead have an error message saying that the file does not exist.