[Wi-Fi] Quit worker thread in WifiNetworkListFragment

Should quit worker thread when a fragment is about to
be destroyed.

Bug: 145100890
Test: make RunSettingsRoboTests ROBOTEST_FILTER=WifiNetworkListFragmentTest
Change-Id: I840750ac4e9601fe553ce219305876581bea7197

src/com/android/settings/wifi/dpp/WifiNetworkListFragment.java

@@ -73,7 +73,7 @@ public class WifiNetworkListFragment extends SettingsPreferenceFragment implemen
     private static final long SCAN_INTERVAL_MILLIS = 10_000;
 
     @VisibleForTesting SavedNetworkTracker mSavedNetworkTracker;
-    private HandlerThread mWorkerThread;
+    @VisibleForTesting HandlerThread mWorkerThread;
 
     // Container Activity must implement this interface
     public interface OnChooseNetworkListener {
@@ -158,6 +158,13 @@ public class WifiNetworkListFragment extends SettingsPreferenceFragment implemen
                 this);
     }
 
+    @Override
+    public void onDestroyView() {
+        mWorkerThread.quit();
+
+        super.onDestroyView();
+    }
+
     @Override
     public void onActivityResult(int requestCode, int resultCode, Intent data) {
         super.onActivityResult(requestCode, resultCode, data);