Fix edges in state machine when dealing with optionals

[smeyer198]

For expressions in the ORDER section of the form (Op1?, Op2)*, the state machine is missing an edge. Currently, there are tree states 0, 1 and 2 with the edges 0 --Op1--> 1, 1 --Op2--> 2, 0 --Op2--> 2 and 2 --Op1--> 1. This forces to use Op1 after using Op2 and being in state 2. However, since Op1 is optional, there is a missing edge 2 --Op2--> 2 that models using Op2 mulitple times. This edge is added with this PR.

Close #295