rod with normals gets tripped up by the NavMesh code

[sebsjames]

This is at runtime. In either the main or modules branches

[14:46:02 build] ./examples/rod_with_normals 
This is version 1.0 of mplot::Visual<glver=4.1> running on OpenGL Version 4.1.0 NVIDIA 580.126.09
right one called
Building NavMesh to save into file /tmp/navmesh_15615617578636428804
Swap order of triangle with he 108
Swap order of triangle with he 114
Swap order of triangle with he 120
Swap order of triangle with he 126
Swap order of triangle with he 132
Swap order of triangle with he 138
Swap order of triangle with he 144
Swap order of triangle with he 150
Swap order of triangle with he 156
Swap order of triangle with he 162
Swap order of triangle with he 168
Swap order of triangle with he 174
Swap order of triangle with he 252
Swap order of triangle with he 255
Swap order of triangle with he 258
Swap order of triangle with he 261
Swap order of triangle with he 264
Swap order of triangle with he 267
Swap order of triangle with he 270
Swap order of triangle with he 273
Swap order of triangle with he 276
Swap order of triangle with he 279
Swap order of triangle with he 282
Swap order of triangle with he 285
0 percent...

Save NavMesh to /tmp/navmesh_15615617578636428804.pre
NavMesh verification test running...
test_neighbours: Found a repeated halfedge that wasn't the first one
36 flag: 2 prev: 38 prev.twin: 106
106 flag: 0 prev: 105 prev.twin: 103
103 flag: 0 prev: 102 prev.twin: 103
The repeat was: 103
Caught exception: Repeated non-start halfedge
[14:46:06 build]