pcb_painter, draw pad clearance outlines: use the pad shape for non copper layers.

For copper layers, if the pad shape is not on the active layer, only the hole
shape clearance is shown (this is correct).
But for non copper layers using the hole shape clearance make no sense
(as long as showing the clearance makes sense for some layers).

pcbnew/pcb_painter.cpp

@@ -1086,13 +1086,23 @@ void PCB_PAINTER::draw( const PAD* aPad, int aLayer )
             const_cast<PAD*>( aPad )->SetSize( pad_size );
     }
 
-    // Clearance outlines
+    // Draw clearance outlines area
     constexpr int clearanceFlags = PCB_RENDER_SETTINGS::CL_PADS;
 
     if( ( m_pcbSettings.m_clearanceDisplayFlags & clearanceFlags ) == clearanceFlags
             && ( aLayer == LAYER_PAD_FR || aLayer == LAYER_PAD_BK || aLayer == LAYER_PADS_TH ) )
     {
-        bool flashActiveLayer = aPad->FlashLayer( m_pcbSettings.GetActiveLayer() );
+        /* Showing the clearance area is not obvious.
+         * - A pad can be removed from some copper layers.
+         * - For non copper layers, what is the clearance area?
+         * So for copper layers, the clearance area is the shape if the pad is on this layer
+         * and the hole clearance area for other coppere layers.
+         * For other layers, use the pad shape, although one can use an other criteria,
+         * depending on the non copper layer
+         */
+        int activeLayer = m_pcbSettings.GetActiveLayer();
+        bool flashActiveLayer = IsCopperLayer( activeLayer ) ?
+                                    aPad->FlashLayer( activeLayer ) : true;
 
         if( flashActiveLayer || aPad->GetDrillSize().x )
         {