show error massage only once

[shawnchenx6]

this patch limited ncm-R to check if nvim-R has started or not only at the startup. So error massage that R is not started will only appear once. it should make things less annoying when people wnat to modify the R code without opening nvim-R.

[olesendan]

Hi. I would like to try this patch, is that possible, when I use gaalcaras's master? I would like to stay on gaalcaras, so I support His work.

EDIT: think I figurered it out, just changed the github source in dein#add()

Greetings from denmark