Fixed AccessibilityServiceInfo.getId()

It was throwing a NPE when the component was not set.

Test: atest android.accessibilityservice.cts.AccessibilityServiceInfoTest

Bug: 271166949
Bug: 271188189

Change-Id: I1755082ff40a9fe037084100ced9286639ffc101

core/java/android/accessibilityservice/AccessibilityServiceInfo.java

@@ -860,10 +860,10 @@ public class AccessibilityServiceInfo implements Parcelable {
      * <p>
      *   <strong>Generated by the system.</strong>
      * </p>
-     * @return The id.
+     * @return The id (or {@code null} if the component is not set yet).
      */
     public String getId() {
-        return mComponentName.flattenToShortString();
+        return mComponentName == null ? null : mComponentName.flattenToShortString();
     }
 
     /**