Fix requesting last messages when no message id is known

[xPaw]

Fixes #1460.

However there's another bug. When doing /clear, the show more button jumps into view, thus IntersectionObserver calls observe on the button, and it loads last history again.

[AlMcKinlay]

When doing /clear, the show more button jumps into view, thus IntersectionObserver calls observe on the button

Hahahaha. That's brilliant.

But that does lead us to a question ... what is the purpose of clear?

I would say either it would clear both client and server side, and therefore have no way to get the stuff back, or it is a pointless feature. Thoughts?

[xPaw]

I don't know either, it sounds like it should clear server buffer too.

[astorije]

what is the purpose of clear?

/clear really acts like clear/ctrl+L in the terminal: it hides / empties the screen, whose content can be brought back by scrolling up.
I actually use it (infrequently) on The Lounge, but I would say a good 60% of the usage I'm making of it can now be achieved by typing /collapse.

I have tried a few things to reproduce this, and nothing worked. Ideally, we would want to be able to set the scrollTop past the maximum, so that latest message is right before the visible block but as far as I know, it's not possible on the web. I have seen a couple "clearable" apps that did that nicely, but they were all native.

Because this is not doable (unless someone has a genius idea), I'd be in favor of removing it.
In fact, even though I use the command myself, I would not like its action to be changed from "hide the latest message" to "destroy all messages in the current channel". That would be a harsh change of an existing feature 😅.
There should be a way to wipe out all the logs for a given channel (in fact, there might be an open issue about this) in a context menu entry for example, but this is a very destructive action that shouldn't be possible with an unfortunate shortcut/command accident lol.

So yeah, until then, I think we should just remove it if there is no way to fix it without drastically changing its behavior.

[xPaw]

Regardless of this clear command bug, this PR fixes the issue on its own, the fact it loads history on clear is a different story, so this can be merged.

[astorije]

That's fair. Is the do not merge label still relevant?