client: Fix Chat Monitor missing sender brackets

client: Fix Chat Monitor missing sender brackets

Always re-add hidden sender brackets for the Chat Monitor as the
normal sender prefixes get replaced with Network, Buffer, and Sender
names.

Sender brackets shown:
> Copy-pasted
  Chat Monitor: <Bitlbee:#channel> digitalcircuit does things
  Channel:      -*- digitalcircuit does things

Before:
> Copy-pasted with sender brackets hidden (wrong)
  Chat Monitor: Bitlbee:#channel digitalcircuit does things
  Channel:      -*- digitalcircuit does things

After:
> Copy-pasted with sender brackets hidden (correct)
  Chat Monitor: <Bitlbee:#channel> digitalcircuit does things
  Channel:      -*- digitalcircuit does things

Closes GH-314.