Gallery2: update content start/end once getUpdateinfo

When viewing last picture in screenshot album and do screenshot, the
new picture will become the first one in album and the album has
changed, but this time current index and content start/end is still
old value, so user will find change to previous picture from current
one in current page.

To aviod this situation, will update content start and content end
once after getUpdateinfo and then can get correct current index and
item path.

CRs-Fixed: 420908

Change-Id: If0da8f8b2ea25d4aed9b8a73f6050e58aadae5de