Theory#moore_dijkstra doesn't play nice with escaping

[josephholsten]

Example script:

#!/usr/bin/env ruby

require 'graphviz'
require 'graphviz/theory'

graph = GraphViz.graph 'escaping-sut' do |g|
  g.add_nodes 'alice@example.com'
  g.add_nodes 'bob@example.com'
  g.add_edges 'alice@example.com', 'bob@example.com'
end

theory = GraphViz::Theory.new graph

route = theory.moore_dijkstra 'alice@example.com', 'bob@simplymeasured.com'

puts "alice -> bob distance: #{route[:distance]}"

Expected result:

alice -> bob distance: 1

Actual result

~/.rbenv/versions/2.1.0-preview1/lib/ruby/gems/2.1.0/gems/ruby-graphviz-1.0.9/lib/graphviz/theory.rb:249:in `block in distance_matrix': undefined method `index' for nil:NilClass (NoMethodError)
    from ~/.rbenv/versions/2.1.0-preview1/lib/ruby/gems/2.1.0/gems/ruby-graphviz-1.0.9/lib/graphviz.rb:233:in `block in each_edge'
    from /Users/joseph/.rbenv/versions/2.1.0-preview1/lib/ruby/gems/2.1.0/gems/ruby-graphviz-1.0.9/lib/graphviz.rb:232:in `each'
    from ~/.rbenv/versions/2.1.0-preview1/lib/ruby/gems/2.1.0/gems/ruby-graphviz-1.0.9/lib/graphviz.rb:232:in `each_edge'
    from /Users/joseph/.rbenv/versions/2.1.0-preview1/lib/ruby/gems/2.1.0/gems/ruby-graphviz-1.0.9/lib/graphviz/theory.rb:248:in `distance_matrix'
    from ~/.rbenv/versions/2.1.0-preview1/lib/ruby/gems/2.1.0/gems/ruby-graphviz-1.0.9/lib/graphviz/theory.rb:72:in `moore_dijkstra'
    from graphs/minimal.rb:15:in `<main>'

Which ends up coming from this line: https://github.com/glejeune/Ruby-Graphviz/blob/v1.0.9/lib/graphviz/theory.rb#L249

x = @graph.get_node(e.node_one( false )).index

Looking at the implementation of Edge#node_one, it is escaping the node id.

But looking at GraphViz#get_node, it's apparent that this function does not expect an escaped value.

A quick search implies that this method is only used in Edge#output, Theory#adjacency_matrix, Theory#incidence_matrix, Theory#degree, and Theory#distance_matrix.

I'd argue that none of the uses in Theory should have the escaping. I think it makes sense to push the escaping into Edge#output.

Does that sound good?