Summary:
SKU required doesn't warn when not filled out
Detailed Description:
If the preference "SKU is required for all items and attributes" is set to YES,
then you go to add an item but don't enter a SKU, no warning message is
displayed. It doesn't submit (which is good) but it isn't obvious to the user
why not.
To recreate:
Set "SKU is required for all items and attributes" to YES in preferences
Add a product, but only fill out the name, then hit submit.