Workflow Designer doesn't expand common transition loops

In JIRA 6.2 global transition loops (those with destination step = -1) got deprecated. They are expanded to ordinary transition loops for each status when the workflow is first opened in the new workflow designer - JRA-38337

However, it appears that common transitions can also be turned into loops by specifying target step=-1. The new WFD doesn't recognise that and fails trying to find a step with ID -1.

Need to expand such common transitions also. We'll convert them into ordinary transition loops for each status that uses the common loop transition.