m_pNetwork from OnUnknownUserRaw is not to be trusted

Don't rely on m_pNetwork it seems to store another user in the
OnUnknownUserRaw ZNC hook and not NULL as expected.

In certain circumstances, the client will send a palaver negotiation
before the registration to ZNC has finished. If this happens,
m_pNetwork value from the module hook could contain a different network
instead of NULL.

If m_pNetwork has another user's network, it would cause this device to be
attached to a different network.

This bug could manifest in a different way, if the network is deleted in the
meantime (once m_pNetwork is set to a network that is deleted). When this
certain code path is run again, it could cause a crash because we would try and
read from memory which has been deallocated.

You may need to delete moddata/palaver/palaver.conf to lose any incorrect
config which was caused by this bug.