Invalid plugin name (control char/backslash) breaks denops.vim

[Milly]

Describe the bug

If you specify a plugin name that contains control characters or backslashes to denops#plugin#load(), an error will occur or it will not work correctly.

Provide a minimal vimrc with less than 50 lines to reproduce

set rtp+=/path/to/github.com/vim-denops/denops.vim
let g:denops#debug = 1
autocmd User DenopsReady call denops#plugin#load("foo\nbar", '/path/to/plugin.ts')

plugin.ts

const main = () => {
  console.log("Hello");
};

How to reproduce the problem from Vim startup

1. Place denops.vim, vimrc and plugin.ts to correct path.
2. Run vim -Nu vimrc.

Expected behavior

If an invalid name is specified, a proper error should be thrown.

Actual behavior

:message

[denops] load plugin: ['foo
[denops] bar', '/path/to/plugin.ts']
[denops] DenopsPluginPre:foo
[denops] DenopsPluginPost:foo
[denops] Failed to emit DenopsSystemPluginPre:foo
[denops] bar: Error: Failed to call 'denops#api#cmd' in Vim: Vim:E492: Not an editor command: bar
[denops] function denops#api#vim#call[2]..denops#api#cmd, line 2
[denops] Failed to emit DenopsSystemPluginPost:foo
[denops] bar: Error: Failed to call 'denops#api#cmd' in Vim: Vim:E492: Not an editor command: bar
[denops] function denops#api#vim#call[2]..denops#api#cmd, line 2

Your environment

• OS: Microsoft Windows [Version 10.0.22631.3880]
• Deno version:

  deno 1.45.0 (release, x86_64-pc-windows-msvc)
  v8 12.7.224.12
  typescript 5.5.2

• Vim/Neovim version:

  VIM - Vi IMproved 9.1 (2024 Jan 02, compiled Jun  1 2024 22:53:51)
  MS-Windows 64-bit GUI version with OLE support
  Included patches: 1-457

• Denops version: commit cfa35fcc7a9326b93ff7e88f71aaee0e71a7cd72 (grafted, HEAD -> v7-pre)