Gallery2: force close happens when remove Gallery widget

The mSource may be null if we destroyed the widget.

So we make the function return null if we remove the
widget to make gallery avoid force closing.

CRs-Fixed: 362477

Change-Id: Ied227235f4dc78aeed69a70c264e523268c344d0
Gallery2: cut some menu items if current page is single item

There is no need to show those items in the menu when we
view this picture in the Mms

Cut some menu items if current page is single item

CRs-Fixed: 379918

Change-Id: I73f7070aebb576c2fe783cbb24f4e6c97a3fc36a