Make polygon built by BOARD::GetBoardPolygonOutlines strictly simple.

It fixes issues in 3d viewer (crashes and incorrect 3D board outline in some cases)

Fixes: lp:167484
https://bugs.launchpad.net/kicad/+bug/1674844

3d-viewer/3d_canvas/cinfo3d_visu.cpp

@@ -484,6 +484,9 @@ void CINFO3D_VISU::createBoardPolygon()
         wxLogMessage( errmsg );
     }
 
+    // Be sure the polygon is strictly simple to avoid issues.
+    m_board_poly.Simplify( SHAPE_POLY_SET::PM_STRICTLY_SIMPLE );
+
     Polygon_Calc_BBox_3DU( m_board_poly, m_board2dBBox3DU, m_biuTo3Dunits );
 }
 

pcbnew/class_board.cpp

@@ -2881,5 +2881,11 @@ extern bool BuildBoardPolygonOutlines( BOARD* aBoard,
 bool BOARD::GetBoardPolygonOutlines( SHAPE_POLY_SET& aOutlines,
                                      wxString* aErrorText )
 {
-    return BuildBoardPolygonOutlines( this, aOutlines, aErrorText );
+    bool success = BuildBoardPolygonOutlines( this, aOutlines, aErrorText );
+
+    // Make polygon strictly simple to avoid issues (especially in 3D viewer)
+    aOutlines.Simplify( SHAPE_POLY_SET::PM_STRICTLY_SIMPLE );
+
+    return success;
+
 }