readline: output of completions when column is undefined

[jasnell]

Per: nodejs/node-v0.x-archive#9001

@ackalker originally reported the issue and @TooTallNate reviewed. Unfortunately
it appears to have stalled. There were a number of issues in the PR that were never
resolved. That said, the issue is still present in master. To reproduce:

bash-3.2$ ./iojs
> process.stdout.columns = undefined;
undefined
> process.std<TAB>

>

(note the blank line after pressing the TAB)

[tyleranton]

I've only ever contributed to doc changes, but I'd like to get into the code. What are the issues with the PR?

[silverwind]

Fixed by e29e470.

@tyleranton Looks like I missed your comment, sorry. This issue already had an pending PR, so would have been a bad candidate. I'll try to flag more issues for contributions in the future.

[tyleranton]

No problem, thanks!