Update `ChannelManager.CurrentChannel` directly to handle non-loaded chat scenario
Update `ChannelManager.CurrentChannel` directly to handle non-loaded chat scenario

`currentChannel` gets instantiated once the chat overlay is open, while
`HighlightMessage` could be called while the chat overlay has never been
open.

This will all be rewritten with the new chat overlay design anyways, so
should be fine for now.

ppy/osu,ppy/osu,peppy/osu,ppy/osu,NeoAdonis/osu,peppy/osu,peppy/osu,NeoAdonis/osu,NeoAdonis/osu