Qt: set the cover art (if any) at CoverArt widget construction

(cherry picked from commit a065e2d9a53b78037f99fa120bf2600aaaac2b85)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/components/interface_widgets.cpp

@@ -519,6 +519,10 @@ CoverArtLabel::CoverArtLabel( QWidget *parent, intf_thread_t *_p_i )
     CONNECT( action, triggered(), this, askForUpdate() );
     addAction( action );
 
+    p_item = THEMIM->currentInputItem();
+    if( p_item )
+        showArtUpdate( p_item );
+    else
         showArtUpdate( "" );
 }