Gallery2: dismiss delete-confirm dialog when pause

If user choose delete operation in camera page mode,
then a confirm dialog will show,then user pause and
resume from pause,will find the dialog still exists
in camera preview.

To prevent confusing user,we will change to dismiss
confirm dialog when pause.

CRs-Fixed: BZ737

Change-Id: Ib22cf78cc6c7e513208f57e502eaf0a4d1f50917