Allow request without product
As it is possible to purchase line without product, it should also be possible to create a request without product. This feature is interesting to implement the purchase requisition module (#5657 (closed)) as this will create purchase request for the user needs which are not always defined as a product in the system (or the purchaser will create the product after on the purchase).
For that we need a new description field which will be required if there is no product selected. But this field should not be filled by default, see #3797 (closed).