Mms: Fix can not mark all messages when checking all

If one conversation contains both SMS and MMS, it will combind query
from both SMS and MMS table, both tables have "_id" column, it will
cause some duplicate item ID in new cursor, the duplicate ID will be
dropped, the duplicate item can not be selected together.

Override getItemId() to get the item ID by position directly.

Change-Id: I2caffe4f6b3dc31201df1ba350dc60e1000941b2
CRs-Fixed: 880464
1 file changed