Orbits have gaps when lines are triangulated

[375gnu]

Describe the bug First I found this bug with #1402 and I realized that I forgot to add NextPos for the last 2 vertices. But it persisted then I checked master and found it there.

To Reproduce Steps to reproduce the behavior:

1. Update Renderer::shouldDrawLineAsTriangles() to always return true or use a device with max line thickness equal to 1px.
2. Enable planet orbits
3. Disable fading orbits
4. Scroll to see all planets of the Solar system.
5. See error

Expected behavior No gaps.

Screenshots

Desktop (please complete the following information):

• OS: any
• Frontend: any
• Version: 1.7.0

Additional context The same orbits with lines drawn as lines doesn't have gaps.

[levinli303]

it seems vec2 transform = normalize(nextPos.xy - thisPos.xy); resulted in nan, as thisPos and nextPos are the same.

[levinli303]

one way to mitigate this issue might be passing in previous point as well, if we see nextPos == thisPos, calculate with prevPos == thisPos.