KML Fix missing domain copyright print

Fix #1911

[Testlink](http://mf-chsdi3.dev.bgdi.ch/shorten/6189cb170b)
It does basically the same as @oterral sample code, but keeping option.attribution and attributions variable as respectively string and object, no? And insuring that what is on the map (attribution) is exactly the same as what is printed (options.attribution). Actually, where do you think there could be a conflict ?