pcbnew: fix incorrect calculation of the board thickness from board stackup.

dielectric sub layers were not taken in account.
Fixes #10899
https://gitlab.com/kicad/code/kicad/issues/10899

pcbnew/board_stackup_manager/board_stackup.cpp

@@ -371,7 +371,16 @@ int BOARD_STACKUP::BuildBoardThicknessFromStackup() const
     for( BOARD_STACKUP_ITEM* item : m_list )
     {
         if( item->IsThicknessEditable() && item->IsEnabled() )
+        {
             thickness += item->GetThickness();
+
+            // dielectric layers can have more than one main layer
+            // add thickness of all sublayers
+            for( int idx = 1; idx < item->GetSublayersCount(); idx++ )
+            {
+                thickness += item->GetThickness( idx );
+            }
+        }
     }
 
     return thickness;

pcbnew/board_stackup_manager/panel_board_stackup.cpp

@@ -428,7 +428,7 @@ wxColor PANEL_SETUP_BOARD_STACKUP::GetSelectedColor( int aRow ) const
 }
 
 
-void PANEL_SETUP_BOARD_STACKUP::computeBoardThickness()
+int PANEL_SETUP_BOARD_STACKUP::computeBoardThickness()
 {
     int thickness = 0;
 
@@ -451,6 +451,8 @@ void PANEL_SETUP_BOARD_STACKUP::computeBoardThickness()
     // The text in the event will translate to the value for the text control
     // and is only updated if it changed
     m_tcCTValue->ChangeValue( thicknessStr );
+
+    return thickness;
 }
 
 

pcbnew/board_stackup_manager/panel_board_stackup.h

@@ -185,8 +185,9 @@ private:
 
     /**
      * Recompute the board thickness and update the textbox
+     * @return the computed value
      */
-    void computeBoardThickness();
+    int computeBoardThickness();
 
     void onColorSelected( wxCommandEvent& event );
     void onMaterialChange( wxCommandEvent& event );