cmdline: incorrect completion if there's text after the cursor

[memchr]

Make sure you have done the following

• Updated to the latest version of blink.cmp
• Searched for existing issues and documentation (try <C-k> on https://cmp.saghen.dev)

Bug Description

When there's text after the cursor, the completion result of next arg is used instead of current arg. This is probably an error in the calculation of arg_number, which causes a wrong query string to be used to call vim.fn.getcompletion().

For example, :lua bit.| vim.api. returns the completion result for the table vim.api instead of bit.

Demo using repro.lua

relevant locals in the demo:

{
  arg_number = 3,
  ['context.line'] = "lua bit. vim.api.",
  current_arg = "vim.api.",
  current_arg_prefix = "vim.api.",
  text_before_argument = "lua bit. "
  query = "lua bit. vim.api."
}

neovim version

v0.10.4

blink.cmp version

main