(Bug) Negative values can be set for price list items

[sfount]

Currently price lists can be set as values or as percentages.

If set as a percentage this will be applied to the sale price of an inventory item, a negative percentage will reduce the price and a positive percentage will increase it.

If set as a value a negative value, this will be allowed by the client - this will be directly set at invoice. Although an invoice cannot be submitted with any value 0 or less this is still set.

Problem
You can set a price list item as a value, less than 0

Expected Behavior
Either the client or server will block a price list item being set as a value and less than 0

[jniles]

@sfount @mbayopanda, who is working on this?