iOS Style: Don't show progress if value is 0

Pick-to: 6.4
Change-Id: I29a29a8b366fd810c41dc8e00e752824d02cd79e
Reviewed-by: Oliver Eftevaag <oliver.eftevaag@qt.io>
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

src/quickcontrols2/ios/ProgressBar.qml

@@ -24,6 +24,7 @@ T.ProgressBar {
 
         readonly property NinePatchImage progress: NinePatchImage {
             parent: control.contentItem
+            visible: control.value
             y: (parent.height - height) / 2
             width: control.indeterminate ? control.width * 0.4 : control.position * parent.width