Inconclusive error message for propti_prepare, line 32

In GitLab by @hehnen1 on Oct 31, 2017, 16:55

While trying to run a modified `input.py` file, starting from the tga example, an `IndexError` ocurred. However, the error message was not helpful, since it didn't provide the file name. Instead it showed `File""`, see below:
```
Traceback (most recent call last):
File "E:GitHub\InverseModeling\propti\propti_prepare.py", line 32, in

exec(open(input_file).read(), globals())
File "", line 254, in
File "", line 254, in
File "", line 239, in create_sim_setup
File "", line 238, in
File "", line 229, in create_relations
IndexError: list index out of range
```