Fix potential null package name

If a client doesn't pass a context, ActivityThread.currentPackageName()
may return null if the client is part of the Android framework. To
ensure logic doesn't break due to a null package name, use
PackageManager.getPackagesForUid() to get a valid package name for the
caller.

Bug: 237725362
Test: Run CHQTS and verify it now passes on a device previously seeing
null package names

Change-Id: Ia706a503f9ca068fc997c0acdcd74ca62a1424be

services/core/java/com/android/server/location/contexthub/ContextHubClientBroker.java

@@ -322,6 +322,17 @@ public class ContextHubClientBroker extends IContextHubClient.Stub
         } else {
             mPendingIntentRequest = new PendingIntentRequest(pendingIntent, nanoAppId);
         }
+
+        if (packageName == null) {
+            String[] packages = mContext.getPackageManager().getPackagesForUid(
+                    Binder.getCallingUid());
+            if (packages != null && packages.length > 0) {
+                packageName = packages[0];
+            }
+            Log.e(TAG, "createClient: Provided package name null. Using first package name "
+                    + packageName);
+        }
+
         mPackage = packageName;
         mAttributionTag = attributionTag;
         mTransactionManager = transactionManager;