go-down-arrow shows wrong unread badge counter sometimes

[r10s]

sometimes, the go-down-arrow shows the unread counter from another chat.

in the following example, there are no unread messages in the selected chat (see chatlist and scrollbar-scrolled-down beside some pixels) - but the badge shows "28 unread messages":

the "28 unread messages" probably comes from the other chat shown one the left. i assume, that was selected before and there was some race.

unfortunately, i cannot offer a clear way to reproduce the bug, it only happens every now and then (but often enough that i file this issue :)

version: 1.46.1 on macos

[Simon-Laux]

strongly related to #3072