Bug: Scrolling with ] in a diff causes the window to close

[jgarte]

Holding down ] to scroll in a diff window causes the window to close so I'm forced to repeatedly press ] to scroll instead of just holding it down.

I'm using

 tig --version
tig version 2.5.6
ncursesw version 6.2.20210619
readline version 8.1

screenshot of the view in which it happens:

[krobelus]

] doesn't really scroll but rather increase the diff context by one.
It recomputes the entire diff which can be expensive.

A proper fix would be to add debouncing logic: recomputing the diff should happen in the background, and each new press of ] would cancel any old operation and start a new one.
Not sure if this is easy to implement. It should be if we are willing to accept a slim possibility of race conditions.