Ensure nets are referenced to main board

We set new elements to the temporary board's netlist.  These need to be
updated when moving the fooprint to the main board

Fixes https://gitlab.com/kicad/code/kicad/-/issues/17242

pcbnew/footprint_libraries_utils.cpp

@@ -927,6 +927,28 @@ bool FOOTPRINT_EDIT_FRAME::SaveFootprintToBoard( bool aAddNew )
                 fixUuid( const_cast<KIID&>( aChild->m_Uuid ) );
             } );
 
+    // Right now, we only show the "Unconnected" net in the footprint editor, but this is still
+    // referenced in the footprint.  So we need to update the net pointers in the footprint to
+    // point to the nets in the main board.
+    newFootprint->RunOnDescendants(
+            [&]( BOARD_ITEM* aChild )
+            {
+                if( BOARD_CONNECTED_ITEM* conn = dynamic_cast<BOARD_CONNECTED_ITEM*>( aChild ) )
+                {
+                    NETINFO_ITEM* net = conn->GetNet();
+                    auto& netmap = mainpcb->GetNetInfo().NetsByName();
+
+                    if( net )
+                    {
+                        auto it = netmap.find( net->GetNetname() );
+
+                        if( it != netmap.end() )
+                            conn->SetNet( it->second );
+                    }
+
+                }
+            } );
+
     BOARD_DESIGN_SETTINGS& bds = m_pcb->GetDesignSettings();
 
     newFootprint->ApplyDefaultSettings( *m_pcb, bds.m_StyleFPFields, bds.m_StyleFPText,