Fix footprint marked as modified when layer visibility changed

Fixes: lp:1830330
* https://bugs.launchpad.net/kicad/+bug/1830330

(cherry picked from commit 741140e4a4)

pcbnew/pcb_layer_widget.cpp

@@ -656,6 +656,8 @@ void PCB_LAYER_WIDGET::OnLayerVisible( int aLayer, bool isVisible, bool isFinal
 
         brd->SetVisibleLayers( visibleLayers );
 
+        // Layer visibility is not stored in .kicad_mod files
+        if( !m_fp_editor_mode )
             myframe->OnModify();
 
         EDA_DRAW_PANEL_GAL* galCanvas = myframe->GetGalCanvas();