Fixing case when TCPServerParameters maxThreads = 0

On pull request #400 the TCP Server was modified to increase (or decrease) ThreadPool size when maxThreads is set on TCPServerParameters. However, when maxThreads = 0 (dafault value) maxThreads should be set to the default pool size (this is done by TCPServrDispatcher, however using the now zeroed pool size!). 

The proposed fix just checks if maxThreads = 0, skipping the pool size change in such case.