Creating edge from target node to source doesn't work correctly

[slimbuck]

If you create an edge starting at a node's outPort dropping on another node's inPort, this works as expected. If the target node is already connected, the existing edge is removed and the new edge created in its place.

However attempting to create the same connection, but starting the target node's inPort and dropping on the source node's outPort, will only work if both ports have no existing clashing edges. If the target node is already connected, then the attempted edge creation will fail.

Starting at the inPort should work the same as starting at the outPort.