Fixed an error when transform node is missing.

[ketoketo]

Fixed the problem so that no error occurs even if the transform node is missing.
When the XML style is fixed, it is not possible to remove unnecessary transform tags, so we had to deal with it programmatically.
I have prepared a sample xml for testing, so please check it out!

https://github.com/benoist/xmldsig/pull/51/files#diff-3cda4c5dd249c588ecc1d75d1a3936ba3b376294492fe083b33a6c883d4f410dR26-R32

[salami96]

This solution closes #55

[Guistoff081]

Hey @benoist, can you check this out? This solves an error which I have been stuck for a few weeks, would be nice to have this merged

[alanBAguero]

@Guistoff081 in the meantime you can monkey patch this module. If you're on a rails app, you can create a file under config/initializers:

require 'xmldsig/transforms/enveloped_signature'

module Xmldsig
  class Transforms < Array
    class EnvelopedSignature < Transform
      def transform
        signatures = node.xpath("descendant::ds:Signature", Xmldsig::NAMESPACES).
          sort { |left, right| left.ancestors.size <=> right.ancestors.size }

        signatures.first&.remove
        node
      end
    end
  end
end