Problem:
with `foldmethod=expr foldexpr=v:lua.vim.treesitter.foldexpr()
foldminlines=0`, deleting lines at the end of the buffer always
reports an invalid top error, because the top value (i.e. the
start line number of the deletion) is always 1 greater than
the total line number of the modified buffer.
Solution:
remove the ml_line_count validation