Steps to reproduce

0. :set splitkeep=screen
1. Set up an autocommand like au FileType qf exe "resize" line('$')
2. Use vim-fugitive's :Ggrep to search for something
3. Open the quickfix window with :cw
4. Use :Ggrep again

At this point I get a

E315: ml_get: Invalid lnum: 1

for some line number that corresponds to the previously active quickfix item.

Expected behaviour

New grep results replace old ones, quickfix is resized

Version of Vim

9.0.662

Environment

OS: Ubuntu 22.04 LTS
Terminal: gnome-terminal
TERM: xterm-256color
shell: bash

Logs and stack traces

Error detected while processing function fugitive#GrepCommand[1]..fugitive#Command[77]..function fugitive#GrepCommand[1]..fugitive#Command[7
0]..<SNR>215_GrepSubcommand[52]..<SNR>215_QuickfixCreate[2]..<SNR>215_QuickfixSet[2]..FileType Autocommands for "*"..function <SNR>30_LoadFT
Plugin[18]..script /home/mg/.vim/ftplugin/qf.vim:
line   31:
E315: ml_get: Invalid lnum: 4

Line 31 of https://github.com/mgedmin/dotvim/blob/master/ftplugin/qf.vim#L31 is

exe "resize" line('$')

vim-fugitive's s:QuickfixSet is doing a
call('setqflist', [], ' ', {'title': ':Ggrep ...'})

I was so far unable to reproduce the issue with vim --clean after setting up autocommands and invoking call setqflist().