OpenDRIVE export: avoid connecting roads with 0-length geometry

[namdre]

There is a mismatch between geometrical length 0 and assigned length of 0.1 for such connecting roads which arises from the sumo network model:

• Whenever two normal edges are connected there is an internal edge to connect them
• Whenever two edges are connected in a straight manner, the can often give "tight" fight with no junction space needed to connect them (giving rise to zero-length geomery)
• Having edges of length 0 would lead to all kinds of anomalies so netconvert simply assigns 0.1

Instead of writing these internal edges as OpenDRIVE connecting road, the two edges should be connected directly.