Fix NPE when removing policies.

Test: atest
android.app.cts.ActivityManagerTest#testTimeTrackingAPI_SimpleStartExit
Fixes: 277978314

Change-Id: I305af84c0fbdffbbcb1f34b1d50ab03476a2e530

services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyEngine.java

@@ -1066,6 +1066,11 @@ final class DevicePolicyEngine {
      * Removes all local policies for the provided {@code userId}.
      */
     private void removeLocalPoliciesForUser(int userId) {
+        if (!mLocalPolicies.contains(userId)) {
+            // No policies on user
+            return;
+        }
+
         Set<PolicyKey> localPolicies = new HashSet<>(mLocalPolicies.get(userId).keySet());
         for (PolicyKey policy : localPolicies) {
             PolicyState<?> policyState = mLocalPolicies.get(userId).get(policy);