Improve error message for empty lots for a shipment when doing stock exit

[jmcameron]

If a shipment selects a specific lot but the lot is exhausted before the Stock Exit for the shipment is performed, currently the item will be quietly dropped from the list of items for the stock exit. A recently merged PR added a generic warning message, but a more detailed warning message would be useful to inform the user exactly which lots were dropped, etc.

Note that this Issue may be related to https://github.com/IMA-WorldHealth/bhima/issues/6413 and https://github.com/IMA-WorldHealth/bhima/issues/6412.