Updating the quantity to produce on a production order will recompute
the expected production duration. This can be counter productive on
prototyping production when no BoM are given. The default expected batch
duration is set to 60 minutes. Setting the actual production time then
updating the quantity to produce will naively change the duration to
60 x the new quantity.
This commit compute the duration pro rata in case of 'no BoM' production
and recompute everything in case of BoM production.
Task : 2278147
William Henrotin
963ad5eada