[BUG] TermExec doesn't work with config.shell = function

[asror1]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

I when trying to use TermExec cmd="some command" I am faced with the following error:

And what ends up happening is the command is not executed.

Expected Behavior

When using config.shell = function, the TermExec should not throw an error, and instead execute the passed in cmd as normal.

Steps To Reproduce

1. In any buffer
2. With the following minimal config:

require("toggleterm").setup({
  shell = function()
    return vim.o.shell
  end,
})

3. Run the following command :TermExec cmd="echo test"
4. And you should see the following error...
   

Environment

- OS: Windows 10
- neovim version: 
NVIM v0.8.2
Build type: RelWithDebInfo
LuaJIT 2.1.0-beta3        
Compiled by runneradmin@fv-az28-353
- Shell: pwsh

Anything else?

I believe this is an easy fix. If I'm not mistaken it comes from using a function for the shell option in the config. I will be submitting a fix PR for this for review.

[akinsho]

fixed by #467