Fix warning when an account is locked

We had all of this wired up correctly in the backend, it just turns out
that we overwrite all messages with "Unlocking failed" immediately.

BUG: 428613

lookandfeel/contents/lockscreen/LockScreenUi.qml

@@ -29,7 +29,10 @@ PlasmaCore.ColorScope {
     Connections {
         target: authenticator
         function onFailed() {
-            root.notification = i18nd("plasma_lookandfeel_org.kde.lookandfeel","Unlocking failed");
+            if (root.notification) {
+                root.notification += "\n"
+            }
+            root.notification += i18nd("plasma_lookandfeel_org.kde.lookandfeel","Unlocking failed");
         }
         function onGraceLockedChanged() {
             if (!authenticator.graceLocked) {
@@ -38,10 +41,10 @@ PlasmaCore.ColorScope {
             }
         }
         function onMessage(msg) {
-            root.notification = msg;
+            root.notification += msg;
         }
         function onError(err) {
-            root.notification = err;
+            root.notification += err;
         }
     }