Add more parent safety checks

Fixes https://gitlab.com/kicad/code/kicad/-/issues/21317

(cherry picked from commit e346139301)

common/widgets/color_swatch.cpp

@@ -326,7 +326,9 @@ void COLOR_SWATCH::GetNewSwatchColor()
 
 void COLOR_SWATCH::OnDarkModeToggle()
 {
-    m_checkerboardBg = m_parent->GetBackgroundColour();
+    wxWindow* parent = GetParent();
+    m_checkerboardBg = parent ? parent->GetBackgroundColour() : wxSystemSettings::GetColour( wxSYS_COLOUR_WINDOW );
 
-    m_swatch->SetBitmap( makeBitmap() );
+    if( m_swatch )
+        m_swatch->SetBitmap( makeBitmap() );
 }

pcb_calculator/calculator_panels/panel_eseries_display.cpp

@@ -70,7 +70,7 @@ PANEL_ESERIES_DISPLAY::PANEL_ESERIES_DISPLAY( wxWindow * parent, wxWindowID id,
     // making the value boxes appear to be separated from each other.
     // Also force text to always be black so it is visible against the light
     // colored cells in both light and dark modes.
-    wxColour gridLineColour = parent->GetBackgroundColour();
+    wxColour gridLineColour = parent ? parent->GetBackgroundColour() : wxSystemSettings::GetColour( wxSYS_COLOUR_WINDOW );
 
     m_GridEseries112->SetDefaultCellTextColour( *wxBLACK );
     m_GridEseries112->SetGridLineColour( gridLineColour );