3d-viewer: Require simplified polygons

3d viewer requires simplified polygons not just for triangulation but
also for its own internal routines.

Fixes: lp:1793085
* https://bugs.launchpad.net/kicad/+bug/1793085

3d-viewer/3d_canvas/create_3Dgraphic_brd_items.cpp

@@ -827,6 +827,8 @@ void CINFO3D_VISU::AddShapeWithClearanceToContainer( const DRAWSEGMENT* aDrawSeg
         aDrawSegment->TransformShapeWithClearanceToPolygon( polyList, aClearanceValue,
                                                         segcountforcircle, correctionFactor );
 
+        polyList.Simplify( SHAPE_POLY_SET::PM_FAST );
+
         if( polyList.IsEmpty() ) // Just for caution
             break;
 
@@ -850,6 +852,10 @@ void CINFO3D_VISU::AddSolidAreasShapesToContainer( const ZONE_CONTAINER* aZoneCo
 {
     // Copy the polys list because we have to simplify it
     SHAPE_POLY_SET polyList = SHAPE_POLY_SET(aZoneContainer->GetFilledPolysList());
+    polyList.Simplify( SHAPE_POLY_SET::PM_FAST );
+
+    if( polyList.IsEmpty() )
+        return;
 
     // This convert the poly in outline and holes
     Convert_shape_line_polygon_to_triangles( polyList,
@@ -857,7 +863,6 @@ void CINFO3D_VISU::AddSolidAreasShapesToContainer( const ZONE_CONTAINER* aZoneCo
                                              m_biuTo3Dunits,
                                              *aZoneContainer );
 
-
     // add filled areas outlines, which are drawn with thick lines segments
     // /////////////////////////////////////////////////////////////////////////
     for( int i = 0; i < polyList.OutlineCount(); ++i )