The new changes for binary payloads for comment diff fragments and page

update payloads attempted to increment the current position by the

parsed next position, instead of setting to that position. This meant

that multiple payloads in a single response resulted in corrupted data

and crashes.
The fix is simply to set the position instead of increment by it.
Along with this, the payload for review request update payloads now

specifies an encoding of utf-8.

New unit tests pass.
Tested manually with a review request that was failing to load

diff comment fragments.