android: fixed crash on calling callback

src/org/adblockplus/android/AdblockPlus.java

 /*
  * This file is part of the Adblock Plus,
  * Copyright (C) 2006-2012 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 953 matching lines @@
           {
             headers[i][0] = header;
             headers[i][1] = StringUtils.join(result.headers.get(header).toArray(), "; ");
             i++;
           }
         }
         params[0] = result.code;
         params[1] = result.message;
         params[2] = headers;
         params[3] = result.data;
+
+        // Do not run callback if engine was stopped
+        if (js == null)
+          return;
+
         js.execute(new Runnable()
         {
           @Override
           public void run()
           {
             js.callback(callback, params);
           }
 
         });
       }
@@ skipping 54 matching lines @@
       }
       return result;
     }
 
     protected void onProgressUpdate(Integer... progress)
     {
       Log.d("HTTP", "Progress: " + progress[0].intValue());
     }
   }
 }