`Zip::FileSystem::ZipFsDir#glob` triggers non-existing `Zip::FileSystem::ZipFileNameMapper#glob` method

Code:

```ruby
require 'zip'
require 'zip/filesystem'

Zip::File.open('archive.zip') do |zip_file|
  zip_file.dir.glob('flags/**/*')
end
```

Output:

```
NoMethodError: undefined method `glob' for #<Zip::FileSystem::ZipFileNameMapper:0x00005654bd818c98>
from /home/alex/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/rubyzip-1.2.1/lib/zip/filesystem.rb:475:in `glob'
```