pcbnew: Check all layers for routing snaps

Flipped footprint pads may report their "primary" layer as not the front
layer in high contrast.  We need to check whether the board item for
snaps is visible on the active layers.

Fixes: lp:1847877
* https://bugs.launchpad.net/kicad/+bug/1847877

pcbnew/router/pns_kicad_iface.cpp

@@ -1071,15 +1071,33 @@ bool PNS_KICAD_IFACE::IsAnyLayerVisible( const LAYER_RANGE& aLayer )
 
 bool PNS_KICAD_IFACE::IsItemVisible( const PNS::ITEM* aItem )
 {
-    if( !m_view )
+    if( !m_view || !aItem->Parent() )
         return false;
 
     auto item = aItem->Parent();
-    auto activeLayers = m_view->GetPainter()->GetSettings()->GetActiveLayers();
-    bool isHighContrast = m_view->GetPainter()->GetSettings()->GetHighContrast();
+    bool isOnVisibleLayer = true;
+
+    if( m_view->GetPainter()->GetSettings()->GetHighContrast() )
+    {
+        int  layers[KIGFX::VIEW::VIEW_MAX_LAYERS];
+        int  layers_count;
+        auto activeLayers = m_view->GetPainter()->GetSettings()->GetActiveLayers();
+
+        isOnVisibleLayer = false;
+        item->ViewGetLayers( layers, layers_count );
+
+        for( int i = 0; i < layers_count; ++i )
+        {
+            // Item is on at least one of the active layers
+            if( activeLayers.count( layers[i] ) > 0 )
+            {
+                isOnVisibleLayer = true;
+                break;
+            }
+        }
+    }
 
-    if( item && m_view->IsVisible( item )
-            && ( !isHighContrast || activeLayers.count( item->GetLayer() ) )
+    if( m_view->IsVisible( item ) && isOnVisibleLayer
             && item->ViewGetLOD( item->GetLayer(), m_view ) < m_view->GetScale() )
         return true;