Line/cable geometry definition: error checking

[PMeira]

The line/cable geometry classes don't include thorough error checking and can cause both crashes and unclear error messages (both in COM and in C-API). They could be extended to at least provide better error messages.

[PMeira]

One recent example from the forum: https://sourceforge.net/p/electricdss/discussion/861976/thread/d22ca64fc2/

There are a bunch more. Some things are simpler to check than others, so we should start doing it.