SWC file without soma points throws

[bsumirak]

Processing a simple SWC file like the following

1 2 0 0 0 6 -1
2 2 10 0 0 2 1
3 2 20 0 0 2 2
4 2 30 0 0 2 3

fails with

ERROR: Caught string exception at top level. message: "CellNetworkIterator::operator->(): down-casting to value type failed. internal logic error."

Changing the structure identifier of the first line to 1 (soma) makes it work.

The code should also work without a soma attached to the geometry.
At least, however, the error should hint to the cause of the problem.

[stephanmg]

After integrating PR #4, AnaMorph will throw with a specific error message, that this is not yet supported.

I think it is best to open a new issue as a feature request for this matter.