Fix issue #128 headers are not written if no rows are written

[ansell]

Fix issue #128 by writing the header during CsvGenerator.close if necessary. See issue comments for discussion so far.

[cowtowncoder]

Excellent!

One process question now: if I haven't yet asked for a Contributor License Agreement:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

I'd need one before merging this. It's only needed once and covers all contributions to Jackson projects.
The usual way is to print, fill & sign, scan, email to info at fasterxml dot com.

Looking forward to merging this fix (I can backport it in 2.7.x) as well.

[ansell]

I haven't signed a CLA yet, will let you know when that process is complete.

[cowtowncoder]

@ansell No problem, thank you for the update.

Also: I gave the link to individual CLA, which most contributors use. But just in case you wanted/needed corporate CLA (sometimes case for big companies; we have 3 from "well-known" big internet companies), there's also that available as

https://github.com/FasterXML/jackson/blob/master/contributor-agreement-corporate.txt