Settings: Fix the force close in ApnEditor

ApnEditor does not call mCursor.moveToFirst() before call
the method mCursor.getInt(ID_INDEX), so the initial position
of cursor is -1.

Add the method mCursor.moveToFirst() in onSaveInstanceState().

CRs-Fixed: 767710

Change-Id: I02a6f1d7aae28aac05f11e7edb2a69ff1b604a13