qml/SliderBar: Apply position inside 'onCompleted'

Calling the state machine signal does not seem to be a good idea given the Connection(s)
items are not fully loaded. This fixes an issue of the Player position not being applied
when loading the SliderBar.

modules/gui/qt/player/qml/SliderBar.qml

@@ -153,9 +153,7 @@ Slider {
         onPositionChanged: fsm.playerUpdatePosition(Player.position)
     }
 
-    Component.onCompleted:  {
-        fsm.playerUpdatePosition(Player.position)
-    }
+    Component.onCompleted: value = Player.position
 
     implicitHeight: control.barHeight
     height: implicitHeight