Reduce SessionItem signaling

• reduce SessionItem signaling regarding sample items
• cleanup/simplify code
• fix warning

GUI/Model/Sample/SampleValidator.cpp

@@ -42,8 +42,8 @@ void SampleValidator::validateItem(const SessionItem* item)
 
 void SampleValidator::validateInterferences(const LayerItem* layer)
 {
-#ifdef WIN32
     ASSERT(layer);
+#ifdef WIN32
 
     int iLayout = 0;
     for (const auto* layout : layer->layouts()) {