Fix the availability of UseOpenWifiPreferenceController.

Right now, it crashes if mEnableUseWifiComponentName is disabled by the
open wifi app.

Bug: 150773571
Test: manual - along with ag/10741759, verified that disabling
mEnableUseWifiComponentName hides the toggle instead of causing crash.
Test: make RunSettingsRoboTests ROBOTEST_FILTER=UseOpenWifiPreferenceControllerTest

Change-Id: I47e36fab411e4e4d1a23b7c91504139f124222e1

src/com/android/settings/wifi/UseOpenWifiPreferenceController.java

@@ -100,6 +100,10 @@ public class UseOpenWifiPreferenceController extends TogglePreferenceController
 
     @Override
     public int getAvailabilityStatus() {
+        // It is possible that mEnableUseWifiComponentName is no longer enabled by
+        // USE_OPEN_WIFI_PACKAGE. So update this component to reflect correct availability.
+        updateEnableUseWifiComponentName();
+        checkForFeatureSupportedScorers();
         return mDoFeatureSupportedScorersExist ? AVAILABLE : CONDITIONALLY_UNAVAILABLE;
     }