Gallery2: Fix crash sometimes when delete video in Gallery.

It's the IndexOutOfBoundsException which causes the app crash.
According to log, it's the size of list is 0, but still want to
get the first item in list.

Add extra judgement before get item from ArrayList, if the size
is 0, skip it as the item is null.

CRs-Fixed: 622574

Change-Id: Ide839b2a73954b9da052a6fece46c864dfa42a21
Merge "Gallery2: Fix crash sometimes when delete video in Gallery." into du44