Don't use centerIn on popup on Qt < 5.12

resources/qml/voip/CallDevices.qml

@@ -5,9 +5,15 @@ import im.nheko 1.0
 
 Popup {
     modal: true
-    anchors.centerIn: parent
     palette: colors
 
+    // only set the anchors on Qt 5.12 or higher
+    // see https://doc.qt.io/qt-5/qml-qtquick-controls2-popup.html#anchors.centerIn-prop
+    Component.onCompleted: {
+        if (anchors)
+            anchors.centerIn = parent;
+    }
+
     ColumnLayout {
         spacing: 16