Fix NPE inside RecentsOrientedState

Bug: 169963211
Change-Id: I86dd337dc1b862f3fa99b91b47fa250076233f96
diff --git a/quickstep/src/com/android/quickstep/util/RecentsOrientedState.java b/quickstep/src/com/android/quickstep/util/RecentsOrientedState.java
index 5f0ef83..bb84380 100644
--- a/quickstep/src/com/android/quickstep/util/RecentsOrientedState.java
+++ b/quickstep/src/com/android/quickstep/util/RecentsOrientedState.java
@@ -539,6 +539,7 @@
      * @return "MyObject@1234"
      */
     private static String extractObjectNameAndAddress(String stringToExtract) {
-        return stringToExtract.substring(stringToExtract.lastIndexOf(DELIMITER_DOT));
+        int index = stringToExtract.lastIndexOf(DELIMITER_DOT);
+        return index >= 0 ? stringToExtract.substring(index) : "";
     }
 }