commerce_discount_set_existing_line_item_price shouldn't use the existing amount.

Problem/Motivation

Found that when adding a commerce order line item that it would use an erroneous amount left over in cache or other that shouldn't when adding a new discount order line item.

commerce_discount_set_existing_line_item_price() calls commerce_discount_add_price_component() which uses existing values.

Proposed resolution

Make another function for setting the order discount price component

commerce_discount_set_price_component

and have commerce_discount_set_existing_line_item_price us that.

Remaining tasks

User interface changes

N/A

API changes

Additional function.