Add PM checker for AppOpsManager

Added null == pm to deal with the possible null pointer problem when
LowRamDevice gets AppOps

Bug:230592908
Fixes:237613199
Test: run gts -m GtsPreserveLegacyStorageHostTest -t android.scopedstorage.cts.host.PreserveLegacyStorageHostTest#testPreserveLegacy

Change-Id: I80f1662a694886ef2acde58ae3eec50254e08aa2

core/java/android/app/AppOpsManager.java

@@ -10291,6 +10291,9 @@ public class AppOpsManager {
 
         // system alert window is disable on low ram phones starting from Q
         final PackageManager pm = context.getPackageManager();
+        if (null == pm) {
+            return AppOpsManager.MODE_DEFAULT;
+        }
         // TVs are constantly plugged in and has less concern for memory/power
         if (ActivityManager.isLowRamDeviceStatic()
                 && !pm.hasSystemFeature(PackageManager.FEATURE_LEANBACK, 0)) {