GF-60069: Allow sequential left key input during transition

toIndex in panels is assigned in startTransition() and becomes 'null' in finishTransition().
That means, toIndex has some value during animating (not null)
And it makes miss judgement to hide panels.

To resolve this matter without any side effects, I add one more
condition which allows left key input during animating.

Enyo-DCO-1.1-Signed-off-by: David Um david.um@lge.com