Keep a bit of spacing in layer tree dock widget

Author: wonder-sk

src/app/qgisapp.cpp

@@ -2353,7 +2353,6 @@ void QgisApp::initLayerTreeView()
 
   QVBoxLayout* vboxLayout = new QVBoxLayout;
   vboxLayout->setMargin( 0 );
-  vboxLayout->setSpacing( 0 );
   vboxLayout->addLayout( toolbarLayout );
   vboxLayout->addWidget( mLayerTreeView );