Zones: fix a crash when adding a zone cutout to a zone having already holes.

Fixes #4039
https://gitlab.com/kicad/code/kicad/issues/4039

libs/kimath/src/geometry/shape_poly_set.cpp

@@ -427,6 +427,8 @@ int SHAPE_POLY_SET::AddHole( const SHAPE_LINE_CHAIN& aHole, int aOutline )
     if( aOutline < 0 )
         aOutline += m_polys.size();
 
+    assert( aOutline < (int)m_polys.size() );
+
     POLYGON& poly = m_polys[aOutline];
 
     assert( poly.size() );

pcbnew/tools/zone_create_helper.cpp

@@ -53,7 +53,7 @@ std::unique_ptr<ZONE_CONTAINER> ZONE_CREATE_HELPER::createNewZone( bool aKeepout
 {
     auto& frame = *m_tool.getEditFrame<PCB_BASE_EDIT_FRAME>();
     auto& board = *m_tool.getModel<BOARD>();
-    BOARD_ITEM_CONTAINER* parent = m_tool.m_frame->GetModel();
+    BOARD_ITEM_CONTAINER* parent = m_tool.m_frame->GetModel();
     KIGFX::VIEW_CONTROLS* controls = m_tool.GetManager()->GetViewControls();
 
     // Get the current default settings for zones
@@ -130,13 +130,18 @@ void ZONE_CREATE_HELPER::performZoneCutout( ZONE_CONTAINER& aZone, ZONE_CONTAINE
     SHAPE_POLY_SET originalOutline( *aZone.Outline() );
     originalOutline.BooleanSubtract( *aCutout.Outline(), SHAPE_POLY_SET::PM_FAST );
 
-    for( int i = 0; i < originalOutline.OutlineCount(); i++ )
+    // After substracting the hole, originalOutline can have more than one
+    // main outline.
+    // But a zone can have only one main outline, so create as many zones as
+    // originalOutline contains main outlines:
+    for( int outline = 0; outline < originalOutline.OutlineCount(); outline++ )
     {
         auto newZoneOutline = new SHAPE_POLY_SET;
-        newZoneOutline->AddOutline( originalOutline.Outline( i ) );
+        newZoneOutline->AddOutline( originalOutline.Outline( outline ) );
 
-        for (int j = 0; j < originalOutline.HoleCount(i) ; j++ )
-            newZoneOutline->AddHole( originalOutline.CHole(i, j), i );
+        // Add holes (if any) to thez new zone outline:
+        for (int hole = 0; hole < originalOutline.HoleCount( outline ) ; hole++ )
+            newZoneOutline->AddHole( originalOutline.CHole( outline, hole ) );
 
         auto newZone = new ZONE_CONTAINER( aZone );
         newZone->SetOutline( newZoneOutline );