TiGLViewer crashes when trailing edge GuideCurve is missing

[LucasKugler]

In some situations, TiGLViewer crashes when a wing has a guide curve defined a the leading edge, but not at the trailing edge.

I have attached a modified verison of the CPACS example simpleAircraft, where i have added guidecurves to the htp. When commenting out one of the TE guide curves from the VTP (l.1107), TiGL fails to render it but does not crash. When doing the same to the HTP (l.1206) however, there is a hard crash.

example_issue#987.zip