key in the multi-material painting gizmo.
Fixed also a similar issue in support and seam gizmos where an object was displayed with the wrong color after pressing the ESC key.
This commit also fixed the following issues:
1) After loading a 3MF with painted triangles using the MMU painting gizmo, the painted triangles might not be displayed correctly in the MMU painting gizmo.
2) The MMU segmentation was unnecessarily executed for all layers and not just for the painted layers.
3) Object's base color wasn't changed when the assigned extruder for that object was changed while the MMU paint gizmo was opened.
4) Changing the base color of an object was only possible by removing all painted triangles.
The cracks were caused by using glPolygonOffset to resolve Z-fighting. All triangles of the object were firstly rendered entirely with a base color. And then paint triangles were drawn over these already rendered triangles.
TriangleSelector::valid refactored to m_valid and valid()
and bool members moved next to each other to shrink data structure
size due to memory alignment.
