Issue 5137 - [emscripten] Added basic filter storage implementation

compiled/storage/FilterStorage.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present 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 100 matching lines @@
   );
   return true;
 }
 
 bool FilterStorage::MoveSubscription(Subscription* subscription,
                                      const Subscription* insertBefore)
 {
   assert(subscription, u"Attempt to move a null subscription"_str);
 
   int oldPos = IndexOfSubscription(subscription);
+  assert(oldPos >= 0, u"Attempt to move a subscription that is not in the list"_str);
   if (oldPos == -1)
-  {
-    assert(subscription, u"Attempt to move a subscription that is not in the list"_str);
     return false;
-  }
 
   int newPos = -1;
   if (insertBefore)
     newPos = IndexOfSubscription(insertBefore);
   if (newPos == -1)
     newPos = mSubscriptions.size();
 
   if (newPos > oldPos)
     newPos--;
 
   if (newPos == oldPos)
     return false;
 
   mSubscriptions.erase(mSubscriptions.begin() + oldPos);
   mSubscriptions.emplace(mSubscriptions.begin() + newPos, subscription);
 
   FilterNotifier::SubscriptionChange(
     FilterNotifier::Topic::SUBSCRIPTION_MOVED,
     subscription
   );
   return true;
 }