QBBSystemLocale: Do not set fixed buffer size when reading pps objects

Set dynamically the buffer size when reading pps objects since a pps file
size is not always fix.

Cherry-picked: qtbase/edf29a9aa93660ac8e4927db7fef2b5d925e9b59

Change-Id: Id55df6a474b6b79d96e3459e807f0bbfeacbf0cb
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>