Fix NPE when querying for already uninstalled package.

It's possible that by the time StorageManagerService receives
the opChanged() callback, the package whose appop was allowed/denied
has already been uninstalled.

Bug: 133442691
Test: manual
Test: atest android.permission2.cts.RestrictedPermissionsTest
Test: atest cts/hostsidetests/appsecurity/src/android/appsecurity/cts/ExternalStorageHostTest.java
Change-Id: Ia032fe174c8796cafffba22036c2afe974c7dea8

services/core/java/com/android/server/StorageManagerService.java

@@ -3597,6 +3597,10 @@ class StorageManagerService extends IStorageManager.Stub
             }
 
             final String[] packagesForUid = mIPackageManager.getPackagesForUid(uid);
+            if (ArrayUtils.isEmpty(packagesForUid)) {
+                // It's possible the package got uninstalled already, so just ignore.
+                return Zygote.MOUNT_EXTERNAL_NONE;
+            }
             if (packageName == null) {
                 packageName = packagesForUid[0];
             }