Signal type of newly added STG transitions may be wrong

[Danil Sokolov]

To reproduce:
1. Add an output transition - its name will be out- and its type will be Output
2. Change the type of signal of this transition to Internal
3. Double-click on the transition and rename it to aaa (without a sign!)
4. Add a new transition - its name will be out- and its type will be Internal

Observed behaviour:
The type of last added transition is Internal

Expected behaviour:
The type of last added transition should be Output