fpm crashes with an exception if a given --workdir path doesn't exist

[jordansissel]

When using the --workdir option, fpm should report an useful and actionable error message if the given path doesn't exist.

Testing with v1.14.2, if the path doesn't exist, fpm throws an exception as follows:

% fpm --workdir /tmp/path/not/exists -s empty -t deb -n example
/home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/stud-0.0.23/lib/stud/temporary.rb:47:in `mkdir': No such file or directory @ dir_s_mkdir - /tmp/path/not/exists/package-empty-build-4b0a05ad8df374a508e46dcb1bfa4d3ab2d966aad5a35de70024a7938234 (Errno::ENOENT)
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/stud-0.0.23/lib/stud/temporary.rb:47:in `directory'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/fpm-1.14.2/lib/fpm/package.rb:267:in `build_path'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/fpm-1.14.2/lib/fpm/package.rb:182:in `initialize'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/fpm-1.14.2/lib/fpm/package/empty.rb:8:in `initialize'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/fpm-1.14.2/lib/fpm/command.rb:309:in `new'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/fpm-1.14.2/lib/fpm/command.rb:309:in `execute'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/clamp-1.0.1/lib/clamp/command.rb:68:in `run'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/fpm-1.14.2/lib/fpm/command.rb:574:in `run'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/clamp-1.0.1/lib/clamp/command.rb:133:in `run'
        from /home/jls/.rbenv/versions/3.1.0/lib/ruby/gems/3.1.0/gems/fpm-1.14.2/bin/fpm:7:in `<top (required)>'
        from /home/jls/.rbenv/versions/3.1.0/bin/fpm:25:in `load'
        from /home/jls/.rbenv/versions/3.1.0/bin/fpm:25:in `<main>'