fix: TermExec cmd with config.shell = function

[asror1]

fixes(#466)

This minor change personally resolves the issue I was facing, although potentially there might be other instances in the code where the shell option is assumed to be a string, I have not looked through the codebase for other occurrences though.

[akinsho]

@asror1 thanks for the PR this looks good, but as you say might miss places where else shell is expected to be a string. I think it would be better to re-assign the value inside of the new or the spawn function similar to how the height and width are derived and stored from functions so that the function is only evaluated once on creation

[asror1]

it would be better to re-assign the value inside of the new or the spawn function similar to how the height and width are derived and stored from functions so that the function is only evaluated once on creation

I've looked through the codebase and the spawn function, or rather the inner __spawn function is already evaluating the shell function before using it.

function Terminal:__spawn()
  local cmd = self.cmd or config.get("shell")
  if type(cmd) == "function" then cmd = cmd() end
  ...

I believe the error was truly just coming the local get_newline_chr() function in the terminal module that is using the shell option directly from config, rather than having it passed in as a parameter. But I'm not sure if it would make sense to have get_newline_chr() accept the shell as parameter, since it is only ever used in the with_cr local func, which in turn is only ever used in Terminal:send method.

[akinsho]

Will merge as is for now since this fixes the issue for now