gui: avoid pre-filling with (0,0) points

[gudeh]

GSOC intern @gs-chaitanya is working on implementing rectlinear floorplans. During his work we noticed a bug, we get a DIE horizontal line going to the origin (0,0) even though the die does not touch the origin:

This PR fixes this issue. I noticed QPolygon initialization is pre-filling its values with multiple (0,0) values, we end up getting double the objects we would need:

  QPolygon[0]: (0, 0)
  QPolygon[1]: (0, 0)
  QPolygon[2]: (0, 0)
  QPolygon[3]: (0, 0)
  QPolygon[4]: (0, 0)
  QPolygon[5]: (0, 0)
  QPolygon[6]: (0, 0)
  QPolygon[7]: (0, 0)
  QPolygon[8]: (0, 0)
  QPolygon[9]: (300000, 20000)
  QPolygon[10]: (300000, 400000)
  QPolygon[11]: (20000, 400000)
  QPolygon[12]: (20000, 600000)
  QPolygon[13]: (800000, 600000)
  QPolygon[14]: (800000, 400000)
  QPolygon[15]: (500000, 400000)
  QPolygon[16]: (500000, 20000)
  QPolygon[17]: (300000, 20000)

Changing the constructor we use, we get the expected values only:

  QPolygonF[0]: (300000.000, 20000.000)
  QPolygonF[1]: (300000.000, 400000.000)
  QPolygonF[2]: (20000.000, 400000.000)
  QPolygonF[3]: (20000.000, 600000.000)
  QPolygonF[4]: (800000.000, 600000.000)
  QPolygonF[5]: (800000.000, 400000.000)
  QPolygonF[6]: (500000.000, 400000.000)
  QPolygonF[7]: (500000.000, 20000.000)
  QPolygonF[8]: (300000.000, 20000.000)

Finally, with the fix we get:

[gudeh]

FYI @eder-matheus @QuantamHD

[gudeh]

I also noticed we use the same constructor type at RenderThread::drawLayer, although I haven't investigated it yet.

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"