Fix 'chosenLabel' callback arg when Custom was chosen without clicking 'Custom' range.

Fixes case where you click the date textboxes to open the calendars
rather than first clicking the word "Custom Range".

Fixup to 430a9607cde57afeafc27ef89410f762924eb571
Merge pull request #279 from elasticsales/fix-custom-label

Fix 'chosenLabel' callback arg