netconvert should not write a network on error

[behrisch]

Currently an exception on writing will create an invalid network. All error checks should probably be done before writing. It seems to affect one check for non-negative speeds and one for the endOffset, see tests/netconvert/function/railway/bidi_endOffset_invalid

[namdre]

it might be easier to delete the network on error (code and performance wise)

[behrisch]

You are too fast ;-) I thought checking beforehand would be better because then the check would not need to be repeated for every output.

[namdre]

checking beforehand slows down writing though. Also, I'm not aware of other writers throwing process errors.

[behrisch]

No, they will simply write faulty networks ;-(