verify spottability before observing for disappearance
verify spottability before observing for disappearance

If the spotted control were disabled, destroyed hidden, etc after it
were spotted but in the same frame, the disappear observers would not
have been set yet (they're async for perf reasons) so an otherwise
unspottable control would be spotted.

Added checks before observing to ensure the spotted control is still
valid.

Issue: ENYO-2706
Enyo-DCO-1.1-Signed-off-by: Ryan Duffy (ryan.duffy@lge.com)

enyojs/spotlight