[Genlist] Fix Genlist item processing issue

[Genlist] Fix Genlist item processing issue

Some applications (ex. music-player) append items on idler or animator
or something. In that case, Later queued items can be processed before
items previously queued because later items can be processed directly
and previous items can be processed on idle enterer.
So if there alreday exist queued items, do not process items directly.

Change-Id: Idf9331f8190e08094a782c4745a76c10578f20a4