app: Put the Placeholder inside the view

If there's more than one main item in the ScrollablePage, QtQuick gets
confused and the placeholder does not get displayed.

(cherry picked from commit e0a64f4a30)

app/qml/FindDevicesPage.qml

@@ -34,12 +34,6 @@ Kirigami.ScrollablePage
         onTriggered: root.refreshing = false
     }
 
-    Kirigami.PlaceholderMessage {
-        text: i18nd("kdeconnect-app", "No devices found")
-        anchors.centerIn: parent
-        visible: devices.count === 0
-    }
-
     ListView {
         id: devices
         section {
@@ -59,6 +53,11 @@ Kirigami.ScrollablePage
                 }
             }
         }
+        Kirigami.PlaceholderMessage {
+            text: i18nd("kdeconnect-app", "No devices found")
+            anchors.centerIn: parent
+            visible: devices.count === 0
+        }
 
         model: DevicesSortProxyModel {
             sourceModel: DevicesModel {}