AbstractQueryChangesTest: avoid possible NPEs on teardown

Change-Id: I517c77fca3a3a40767137296dc55d129855af809
diff --git a/gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java b/gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
index e89e3fe..9829c98 100644
--- a/gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
+++ b/gerrit-server/src/test/java/com/google/gerrit/server/query/change/AbstractQueryChangesTest.java
@@ -118,9 +118,13 @@
 
   @After
   public void tearDownInjector() {
-    lifecycle.stop();
+    if (lifecycle != null) {
+      lifecycle.stop();
+    }
     requestContext.setContext(null);
-    db.close();
+    if (db != null) {
+      db.close();
+    }
     InMemoryDatabase.drop(schemaFactory);
   }