Do not try to read from UI elements that haven't been initialized yet

Fixes https://gitlab.com/kicad/code/kicad/-/issues/13480

pcbnew/board_stackup_manager/panel_board_stackup.cpp

@@ -1315,6 +1315,10 @@ void PANEL_SETUP_BOARD_STACKUP::ImportSettingsFrom( BOARD* aBoard )
 
 void PANEL_SETUP_BOARD_STACKUP::OnLayersOptionsChanged( LSET aNewLayerSet )
 {
+    // Can be called spuriously from events before the layers page is even created
+    if( !m_panelLayers->IsInitialized() )
+        return;
+
     // First, verify the list of layers currently in stackup:
     // if it does not mach the list of layers set in PANEL_SETUP_LAYERS
     // rebuild the panel

pcbnew/dialogs/panel_setup_layers.cpp

@@ -128,7 +128,8 @@ PANEL_SETUP_LAYERS::PANEL_SETUP_LAYERS( PAGED_DIALOG* aParent, PCB_EDIT_FRAME* a
         PANEL_SETUP_LAYERS_BASE( aParent->GetTreebook() ),
         m_parentDialog( aParent ),
         m_frame( aFrame ),
-        m_physicalStackup( nullptr )
+        m_physicalStackup( nullptr ),
+        m_initialized( false )
 {
     m_pcb = aFrame->GetBoard();
 }
@@ -248,6 +249,8 @@ bool PANEL_SETUP_LAYERS::TransferDataToWindow()
     setMandatoryLayerCheckBoxes();
     setUserDefinedLayerCheckBoxes();
 
+    m_initialized = true;
+
     return true;
 }
 

pcbnew/dialogs/panel_setup_layers.h

@@ -91,6 +91,8 @@ public:
         m_physicalStackup = aPanel;
     }
 
+    bool IsInitialized() const { return m_initialized; }
+
 private:
 
     void setLayerCheckBox( int layer, bool isChecked );
@@ -132,6 +134,7 @@ private:
     PANEL_SETUP_BOARD_STACKUP* m_physicalStackup;
     BOARD*                     m_pcb;
     LSET                       m_enabledLayers;
+    bool                       m_initialized;
 };