Fixes ENYO-723

## Issue
`_marquee_calcDistance` expects a valid node to measure its natural and clipped dimensions. In cases where the control hasn't been generated but a marquee has been requested (e.g. an onRequestMarqueeStart event waterfalled down from a containing contro), this measurement fails.

## Fix
Prevent starting marquee when the control hasn't been generated

Enyo-DCO-1.1-Signed-off-by: Ryan Duffy (ryan.duffy@lge.com)