The restart command should start the server if it's not yet running

**Is your feature request related to a problem? Please describe.**

I sometimes forget I already stopped the language server, and run the "Restart Haskell LSP server" command instead of "Start Haskell LSP server" command. This results in the following (kinda cryptic) error popup:


I assume this happens because whatever API the plugin is using expects an existing process to stop and then start.

I of course know now that I should then use the "start" command instead, but it was confusing the first few times and makes the plugin feel less polished than it should be.

**Describe the solution you'd like**

Ideally "Restart" should just start the language server if it's not yet running, instead of showing an error; the most I'd expect is an unobtrusive warning or the like saying "hey, the server wasn't running yet so I just started it."

**Describe alternatives you've considered**

One alternative is showing a more descriptive error message, e.g. instead of "call listen() first" it could say "use the start command instead of restart".

**Additional context**

None I can think of.