Packet headers are not zero-encoded so don't try to zero-decode these in PacketPool.GetType()

Instead adjusts code with that from Packet.BuildHeader(byte[], ref int, ref int):Header in libomv
This stops packet decoding failures with agent UUIDs that contain 00 in their earlier parts (e.g. b0b0b0b0-0000-0000-0000-000000000211)
Thanks to lkalif for pointing this out.