jupyter-repl-mode chokes if yank-excluded-properties is not a list

[mcmillanbb]

In the setup for jupyter repl mode, there is a call to remq on yank-excluded-properties.
This assumes that yank-excluded-properties is a list. However, the variable yank-excluded-properties allows for the value of t, in which case jupyter repl mode cannot start up.

It should be a minor fix, simply wrapping the call in a check that yank-excluded-properties is a list.
If that makes sense, I am happy to submit a pull request.

[nnicandro]

Sounds good,for the case of t just (and yank-excluded-properties nil) should be good enough.

[mcmillanbb]

I'm sorry, I don't quite understand your comment, can you expand a little?

[tgbugs]

See #408

[mcmillanbb]

Ah, thanks for pointing that out! I thought I had searched for the issue, but must have missed yours.
Your PR would would work for me.