Fix edit variables

[szaffarano]

Fixes #349

As reported by the linked issue, editing variables shows an error, although it works as expected. The problem was that it wasn't capturing the first pcall return value (aka success) to figure out whether the pcall worked or not, and then, yes, use its second return value (aka result) to eventually handle the error. More info: http://www.lua.org/manual/5.1/manual.html#pdf-pcall

[myth0genesis]

This worked for me on Windows 11 and Neovim 0.10.0.

[rcarriga]

Thanks for the PR! :smile: