Fix some warnings

src/app/qgsfeatureaction.cpp

@@ -223,6 +223,7 @@ bool QgsFeatureAction::addFeature( const QgsAttributeMap& defaultAttributes )
 void QgsFeatureAction::onFeatureSaved( const QgsFeature& feature )
 {
   QgsAttributeForm* form = qobject_cast<QgsAttributeForm*>( sender() );
+  Q_UNUSED( form ) // only used for Q_ASSERT
   Q_ASSERT( form );
 
   mFeatureSaved = true;

src/gui/qgsattributeform.cpp

@@ -245,6 +245,7 @@ void QgsAttributeForm::onAttributeChanged( const QVariant& value )
 
 void QgsAttributeForm::onAttributeAdded( int idx )
 {
+  Q_UNUSED( idx ) // only used for Q_ASSERT
   if ( mFeature.isValid() )
   {
     QgsAttributes attrs = mFeature.attributes();