Fix NPE issue in Internet Settings

- Ignore onWifiEntriesChanged callback when Activity does not exist

Bug: 389552565
Flag: EXEMPT bugfix
Test: Manual testing
atest -c NetworkProviderSettingsTest

Change-Id: I031043616f7c38d4bb27aa81ae3a0a0a32991c62

src/com/android/settings/network/NetworkProviderSettings.java

@@ -924,6 +924,9 @@ public class NetworkProviderSettings extends RestrictedDashboardFragment
 
     @Override
     public void onWifiEntriesChanged(@WifiPickerTracker.WifiEntriesChangedReason int reason) {
+        if (isFinishingOrDestroyed()) {
+            return;
+        }
         updateWifiEntryPreferences();
         if (reason == WifiPickerTracker.WIFI_ENTRIES_CHANGED_REASON_SCAN_RESULTS) {
             setProgressBarVisible(false);