New events from a gappy sync are not displayed in the timeline when scrolled up

[bwindels]

If scrolled up in the timeline and receiving a gappy sync, the new events are not displayed in the timeline.
Seems to be related to the canResetTimeline logic that requires being scrolled all the way down to reset the timeline.
I'm repro-ing this with a e2e test.

[bwindels]

From riot:
Bruno: btw, yesterday I was looking into why the timeline doesn't get rendered in an e2e test after a gappy sync. It turned out to be the canResetTimeline() logic, which checks if you're at the bottom of the timeline (the e2e was scrolled all the way up, hence failing). Why is it unsafe though to reset the timeline when not scrolled to the bottom? Because you could see apart of the timeline disappear in front of your eyes? Still feels a bit like a bug to not show those messages at all if you're not scrolled to the bottom ...

[lampholder]

I've put a lazy-loading label on this guy - please remove it if it's not appropriate :)

[bwindels]

As far as I can tell, it's not related to lazy loading.