Implemented proper validation of variable-length packets.

Also changed output buffer in pcAttackNpcs() from dynamically to
statically allocated. This in itself is temporary as I have a better
idea as to how we can allocate buffers with a bit less boilerplate.

src/CNProtocol.cpp

@@ -170,7 +170,7 @@ void CNSocket::step() {
             // we got out packet size!!!!
             readSize = *((int32_t*)readBuffer);
             // sanity check
-            if (readSize > MAX_PACKETSIZE) {
+            if (readSize > CN_PACKET_BUFFER_SIZE) {
                 kill();
                 return;
             }