Don't crash if default supervision profile owner is not set

Bug: 175430552
Test: build, flash, watch logcat

Change-Id: If441946fa278c04ae88122f6243f5a7dedd96ebc
(cherry picked from commit bd27c365915f824824d865668c63a2119c4700fb)
diff --git a/services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java b/services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java
index 1a2eee0..ac2281a 100644
--- a/services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java
+++ b/services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java
@@ -8817,6 +8817,9 @@
                 return null;
             }
             final ComponentName supervisorComponent = ComponentName.unflattenFromString(supervisor);
+            if (supervisorComponent == null) {
+                return null;
+            }
             if (supervisorComponent.equals(doComponent) || supervisorComponent.equals(
                     poComponent)) {
                 return supervisorComponent;