bug: normal-mode `,mq` (Quote) crashes when no prior visual selection — line("'<") returns 0 not nil

[monkeyxite]

Reproduce

In a mail buffer, without having made any visual selection first, press ,mq in normal mode.

Result

E5108: Lua: .../nvim-mail/init.lua:123: 'start' is higher than 'end'
stack traceback:
        [C]: in function 'nvim_buf_set_lines'
        .../nvim-mail/init.lua:123: in function <.../nvim-mail/init.lua:116>

Root cause

lua/nvim-mail/init.lua lines 117-118 (normal-mode Quote handler):

local start_line = vim.fn.line("'<") or vim.fn.line('.')
local end_line   = vim.fn.line("'>") or vim.fn.line('.')

When the '< / '> marks are unset, vim.fn.line() returns 0, not nil. Since 0 is truthy in Lua, the or fallback never fires. This leaves start_line = 0 and end_line = 0, so the call becomes:

vim.api.nvim_buf_set_lines(0, -1, 0, false, lines)

start = -1 counts from the end of the buffer (= last line), end = 0, so start > end → E5108.

Scope

Only the normal-mode variant is affected. The visual-mode variant at lines 128-129 is safe because '< / '> are guaranteed set when a visual-mode mapping fires.

Proposed fix

Explicit zero-check on the mark lookup:

map('q', function()
  local start_line = vim.fn.line("'<")
  if start_line == 0 then start_line = vim.fn.line('.') end
  local end_line = vim.fn.line("'>")
  if end_line == 0 then end_line = vim.fn.line('.') end
  -- ... rest unchanged
end, ' Quote')

Alternative design worth considering: the normal-mode ,mq currently reads stale visual marks (which may point at an unrelated line from a prior visual selection). Arguably normal-mode ,mq should just quote the current line (line('.') for both start and end) and not consult '< / '> at all. That would be the less-surprising behavior.

Suggested test

Add to tests/mail/init_spec.lua (or wherever quote tests belong): open a mail fixture, do not enter visual mode, call the normal-mode ,mq handler directly. Assert no error is raised and the current line gets a > prefix.

Related audit

Grepped the whole lua/nvim-mail/ tree for vim.fn.line("'<") / vim.fn.line("'>") / getpos and or vim.fn.line — only these two lines match. No wider family of the same bug.