Fix divide-by-zero vulnerability in scroll_cursor_bot.

[fullwaywang]

Fix #12528

[brammool]

Please fix test_codestyle (move the "{" to the next line).

In the test, I wonder why you need to disable "wait_for_ruler"? It makes the test less reliable.
In that same place, why use 19 rows? Can't we use something smaller, e.g. 10 rows?

[fullwaywang]

Hi, code style has been fixed :)

As for the wait_for_ruler option, I just kept it as same as the test for the fix of CVE-2023-0512. I did made an experiment, though, that without disabling wait_for_ruler, the single test would take 5 secs and fail. Not sure whether this is because vsplit is on or -g -O0 is configured in my experimental environment. After disabling it the test passes fine.

As for the 19 rows, well, it is an experimental value. In this specific, I need to ensure the curwin width is smaller than the line-number column width, so I put more than 10 empty lines there, and it worked.

[codecov]

Codecov Report

Merging #12540 (e6db8a9) into master (166cd7b) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12540      +/-   ##
==========================================
+ Coverage   82.07%   82.09%   +0.01%     
==========================================
  Files         160      160              
  Lines      193641   193651      +10     
  Branches    43480    43482       +2     
==========================================
+ Hits       158938   158983      +45     
+ Misses      21859    21833      -26     
+ Partials    12844    12835       -9     

Flag	Coverage Δ
huge-clang-none	82.72% <100.00%> (-0.02%)	⬇️
linux	82.72% <100.00%> (-0.02%)	⬇️
mingw-x64-HUGE	76.61% <0.00%> (+<0.01%)	⬆️
mingw-x86-HUGE	77.06% <0.00%> (+<0.01%)	⬆️
windows	78.19% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/move.c	92.55% <100.00%> (+<0.01%)	⬆️

... and 20 files with indirect coverage changes