'Invalidpoint' error

[rcb8890]

I've tried to use your script to dogbone a closed curve - but I get an error 'invalidpoint' when I try clicking on the points in this closed curve, which I've put on a layer called 'broken curves.'

The script works for curves I draw from scratch. The broken curves have been split and joined many times, but are recognised as valid closed curves.

Wondering if there's something obvious I'm missing? Test file here.

Any help appreciated! :)