Fixed a bug introduced in #218 causing packet loops. FIXES 202.

In 659f01cc632617f5e2e23cd097fbec81fce7dc1a, I attempted to 
execute packet listeners for receiveClientPacket() on the channel
thread, inadvertently causing them to be executed regardless if 
filtered was FALSE, and twice if it is TRUE.

Since asynchronous packet listeners use this feature to take out
packets from the packet stream, they wound up causing an infinite 
packet loop. This prevented them from ever being received by the
server.