[web] Fix fetching messages in messages list
Summary:
When there were more than 40 messages in a thick thread, fetching more messages sometimes resulted in fetching more batches at once and jumping back a multiple of 20 messages. This issue was caused by an old bugfix that was fixing an issue where an empty space was displayed after opening a thread, when it had more than 20 messages https://github.com/CommE2E/comm/commit/0639b7628833dd318f58fb7ed36538dac75336a4. The solution to this is to apply this bugfix only when we initially open the page - this can be tested by checking if a scroll position is 0.
Test Plan:
Created a thread with 200 messages. Tested on Chrome and Safari.
- Opened the web page and scrolled slowly near every 20th messages. The original issue happened about 50% of the times, so I made sure to test it a couple of times. Didn't experience any glitches.
- Zoomed out so that more than 20 messages can be seen at once and opened the web app. Immediately after opening the app more messages were fetched.
Reviewers: kamil, inka, ashoat
Reviewed By: ashoat
Differential Revision: https://phab.comm.dev/D13634