VeSTige: set VeSTige logo as window icon for plugin GUI subwindow

Up to now the MainWindow's icon was used for VST plugin GUI subwindows.
Improve this a little bit by using the VeSTige logo now.
(cherry picked from commit 5e711875f5)

plugins/vestige/vestige.cpp

@@ -348,6 +348,11 @@ void VestigeInstrumentView::openPlugin( void )
 		engine::getMixer()->lock();
 		m_vi->loadFile( ofd.selectedFiles()[0] );
 		engine::getMixer()->unlock();
+		if( m_vi->m_plugin && m_vi->m_plugin->pluginWidget() )
+		{
+			m_vi->m_plugin->pluginWidget()->setWindowIcon(
+									PLUGIN_NAME::getIconPixmap( "logo" ) );
+		}
 	}
 }