fix(actions): allow bufnr to be 0

[igorlfs]

Problem: documentation mentions that bufnr can be 0 for get_hunks, but 0 is truthy, so the current logic does not work

Solution: properly check if the current buf should be used (same logic as vim._resolve_bufnr)

I also took the liberty of updating the type annotations to be more precise.

---

There are two other instances where the same logic is being used, but for them, 0 is not documented as being the current buf (so I haven't updated them):

gitsigns.nvim/lua/gitsigns/attach.lua

Lines 413 to 431 in 1ee5c1f

	--- Detach Gitsigns from the buffer {bufnr}. If {bufnr} is not
	--- provided then the current buffer is used.
	---
	--- @param bufnr integer Buffer number
	--- @param keep_signs? boolean
	function M.detach(bufnr, keep_signs)
	-- When this is called interactively (with no arguments) we want to remove all
	-- the signs, however if called via a detach event (due to nvim_buf_attach)
	-- then we don't want to clear the signs in case the buffer is just being
	-- updated due to the file externally changing. When this happens a detach and
	-- attach event happen in sequence and so we keep the old signs to stop the
	-- sign column width moving about between updates.
	bufnr = bufnr or api.nvim_get_current_buf()
	dprint('Detached')
	local bcache = cache[bufnr]
	if not bcache then
	dprint('Cache was nil')
	return
	end

gitsigns.nvim/lua/gitsigns/actions.lua

Lines 71 to 95 in 1ee5c1f

	--- Attach Gitsigns to the buffer.
	---
	--- Attributes: ~
	--- {async}
	---
	--- @param bufnr integer Buffer number
	--- @param ctx Gitsigns.GitContext|nil
	--- Git context data that may optionally be used to attach to any
	--- buffer that represents a real git object.
	--- • {file}: (string)
	--- Path to the file represented by the buffer, relative to the
	--- top-level.
	--- • {toplevel}: (string?)
	--- Path to the top-level of the parent git repository.
	--- • {gitdir}: (string?)
	--- Path to the git directory of the parent git repository
	--- (typically the ".git/" directory).
	--- • {commit}: (string?)
	--- The git revision that the file belongs to.
	--- • {base}: (string?)
	--- The git revision that the file should be compared to.
	--- @param _trigger? string
	M.attach = async.create(3, function(bufnr, ctx, _trigger)
	require('gitsigns.attach').attach(bufnr or api.nvim_get_current_buf(), ctx, _trigger)
	end)