fix updating of the media component

nymea-app/ui/mainviews/GroupsView.qml

@@ -386,7 +386,8 @@ MouseArea {
                 shownInterfaces: ["mediacontroller"]
             }
 
-            device: mediaControllers.parentProxy ? mediaControllers.get(0) : null
+            // involve count in the statement to make the binding re-evaluate when the group is changed
+            device: mediaControllers.count > 0 ? mediaControllers.get(0) : null
         }
     }
 }