/process_receipt_approval/: Fix a thinko
/process_receipt_approval/: Fix a thinko

The pos variable that tracks the position within the POST data wasn't
being initialised and was just remembering its last value, thus once
you'd processed one lot of receipts, subsequent calls would just return
as pos was pointing to the end of the POST data.

Initialise pos to 0 at declaration time.

Signed-off-by: Andrew Clayton <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@opentechlabs.co.uk>

ac000/receiptomatic