Large telnet option sequences are not properly processed

[ctoth]

In src/network.cc line 464 if a telnet sequence does not end before the end of a single packet it is both ignored, and then further content is read as if it were a regular command, corrupting the next command.

Telnet option sequences can be longer than a single packet, and so this is not working correctly.

We may explore using libtelnet rather than implementing our own state machine to parse this properly, but that has its own downsides, as Libtelnet seems to want to fully take over the connection and we still want to be able to handle telnet commands in-MOO.