Gerbview: clear all previous highlight selections, after clearing all layers.

Fixes #8893
https://gitlab.com/kicad/code/kicad/issues/8893

gerbview/gerbview_painter.cpp

@@ -104,6 +104,15 @@ void GERBVIEW_RENDER_SETTINGS::LoadDisplayOptions( const GBR_DISPLAY_OPTIONS& aO
 }
 
 
+void GERBVIEW_RENDER_SETTINGS::ClearHighlightSelections()
+{
+    // Clear all highlight selections (dcode, net, component, attribute selection)
+    m_componentHighlightString.Empty();
+    m_netHighlightString.Empty();
+    m_attributeHighlightString.Empty();
+    m_dcodeHighlightValue = -1;
+}
+
 COLOR4D GERBVIEW_RENDER_SETTINGS::GetColor( const VIEW_ITEM* aItem, int aLayer ) const
 {
     const EDA_ITEM* item = dynamic_cast<const EDA_ITEM*>( aItem );

gerbview/gerbview_painter.h

@@ -129,6 +129,9 @@ public:
         return m_diffMode;
     }
 
+    /// Clear all highlight selections (dcode, net, component, attribute selection)
+    void ClearHighlightSelections();
+
     /// If set to anything but an empty string, will highlight items with matching component
     wxString m_componentHighlightString;
 

gerbview/tools/gerbview_control.cpp

@@ -165,10 +165,7 @@ int GERBVIEW_CONTROL::HighlightControl( const TOOL_EVENT& aEvent )
         m_frame->m_SelNetnameBox->SetSelection( 0 );
         m_frame->m_SelAperAttributesBox->SetSelection( 0 );
 
-        settings->m_netHighlightString = "";
-        settings->m_componentHighlightString = "";
-        settings->m_attributeHighlightString = "";
-        settings->m_dcodeHighlightValue = -1;
+        settings->ClearHighlightSelections();
 
         GERBER_FILE_IMAGE* gerber = m_frame->GetGbrImage( m_frame->GetActiveLayer() );
 
@@ -321,6 +318,11 @@ int GERBVIEW_CONTROL::ClearAllLayers( const TOOL_EVENT& aEvent )
     canvas()->Refresh();
     m_frame->ClearMsgPanel();
 
+    // Clear pending highlight selections, now outdated
+    KIGFX::GERBVIEW_RENDER_SETTINGS* settings =
+            static_cast<KIGFX::GERBVIEW_PAINTER*>( getView()->GetPainter() )->GetSettings();
+    settings->ClearHighlightSelections();
+
     return 0;
 }