BUG: joint definition

[DanielePlacidoPolito]

Describe the bug
Flag ISJOINT and related parameters XJBEG, XJBEIN XJBEOUT XJENOUT do not work.

To Reproduce
Steps to reproduce the behavior:

1. Go to conductor_definition.xlsx
2. Click on sheet CONDUCTOR_input
3. Scroll down to row 13 up to 17
4. Assign values to the parameters
5. Save and run the software
6. See error

Expected behavior
OPENSC2 should keep into account the joint.

Desktop (please complete the following information):

• OS: Windows 10