Fix an NPE as DownloadManager.query() could return a null cursor

chrome/android/java/src/org/chromium/chrome/browser/download/DownloadManagerDelegate.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.download;
 
 import android.app.DownloadManager;
 import android.content.Context;
 import android.database.Cursor;
 import android.os.AsyncTask;
@@ skipping 80 matching lines @@
             mShowNotifications = showNotifications;
             mCallback = callback;
         }
 
         @Override
         public DownloadQueryResult doInBackground(Void... voids) {
             DownloadManager manager =
                     (DownloadManager) mContext.getSystemService(Context.DOWNLOAD_SERVICE);
             Cursor c = manager.query(
                     new DownloadManager.Query().setFilterById(mDownloadItem.getSystemDownloadId()));
+            if (c == null) {
+                return new DownloadQueryResult(mDownloadItem,
+                        DownloadManagerService.DOWNLOAD_STATUS_CANCELLED, 0, 0, false, 0);
+            }
             long bytesDownloaded = 0;
             boolean canResolve = false;
             int downloadStatus = DownloadManagerService.DOWNLOAD_STATUS_IN_PROGRESS;
             int failureReason = 0;
             long lastModifiedTime = 0;
             if (c.moveToNext()) {
                 int statusIndex = c.getColumnIndex(DownloadManager.COLUMN_STATUS);
                 int status = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
                 if (status == DownloadManager.STATUS_SUCCESSFUL) {
                     downloadStatus = DownloadManagerService.DOWNLOAD_STATUS_COMPLETE;
@@ skipping 19 matching lines @@
             return new DownloadQueryResult(mDownloadItem, downloadStatus, totalTime,
                     bytesDownloaded, canResolve, failureReason);
         }
 
         @Override
         protected void onPostExecute(DownloadQueryResult result) {
             mCallback.onQueryCompleted(result, mShowNotifications);
         }
     }
 }