Weird break in some cross-sections

[StephenNneji]

This issue is a bug report

• What is the current behaviour?
  A weird break appears in some cross-sections in the graphics selection window

• If the current behaviour is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

1. Open the collide.h5 example project
2. Open the graphic selection window, Click Insert > Measurement Point > Graphic Selection
3. Change the plane normal to Custom Normal and set the normal to [1, 1, 1]
4. Set the plane distance to 158.770, the cross-section should be as shown below with no breaks (first image)
5. Set the plane distance to 158.771, the cross-section shows a break (second image)

• What is the expected behaviour?
  There should be no break

• Please tell about the environment(s) affected:
  All

• Other information (e.g. detailed explanation, screenshots, stack traces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, gitter, etc):