Honor javadocs, call super first in DocumentsProvider.call handling.

package com.android.documentsui;

import static com.android.documentsui.Shared.TAG;

import android.annotation.NonNull;

import android.annotation.Nullable;

import android.content.Context;

import android.content.SharedPreferences;

import android.content.pm.ProviderInfo;

    @Override

    public Bundle call(String method, String arg, Bundle extras) {

        // We're not supposed to override any of the default DocumentsProvider

        // methods that are supported by "call", so javadoc asks that we

        // always call super.call first and return if response is not null.

        Bundle result = super.call(method, arg, extras);

        if (result != null) {

            return result;

        }

        switch (method) {

            case "clear":

                clearCacheAndBuildRoots();

                simulateReadErrorsForFile(arg);

                return null;

            case "createDocumentWithFlags":

                Bundle bundle = dispatchCreateDocumentWithFlags(extras);

                return bundle;

            default:

                return super.call(method, arg, extras);

                return dispatchCreateDocumentWithFlags(extras);

        }

        return null;

    }

    private Bundle createVirtualFileFromBundle(Bundle extras) {