WINTERMUTE: Fix for unnecessary "WARNING: getChildren() failed for path:"

FSNode::getChildren() was called assuming that it returns 0 iff success.
Actually, it's the other way around.
WINTERMUTE: Prevent warning about duplicate files when autodetecting.

Removed a call to BaseFileManager::registerPackages() in
WintermuteEngine::getGameInfo(), as the constructor for BaseFileManager
already calls registerPackages() once; another call should thus be
superfluous.