Fix NPE on ActivityStack.removeTask when launched with invalid taskId

Prevents NPE in removeTask when use getDisplay directly.

Bug: 119023840
Test: atest WmTests:ActivityStackTests

Change-Id: I894f4b13e8a61c267f51af5331d8524a26cea009

services/core/java/com/android/server/wm/ActivityStack.java

@@ -5438,7 +5438,7 @@ class ActivityStack extends ConfigurationContainer {
             if (isAttached()) {
                 getDisplay().positionChildAtBottom(this);
             }
-            if (!isActivityTypeHome() || getDisplay().isRemoved()) {
+            if (!isActivityTypeHome() || !isAttached()) {
                 remove();
             }
         }