New drop ship SO line needs to be added to the existing Dropship PO created.

Summary:

Use Case: Adding new line to the existing Dropship SO should add new PO line to the existing dropship PO.

Behavior: When adding new line to the existing dropship sales order, creates a separate Dropship PO.

Expectation: When adding new line to the existing Dropship sales order, in purchasing the new line should get added to the existing dropship PO which was created for other lines of Dropship Sales order

Steps to reproduce:

1. Create a dropship SO (SO1) with 2 line (Line1 and Line2).

2. Progress the order and status is Awaiting Shipping.

3. Dropship PO (PO1) is created with 2 lines (Line1 and Line2) from dropship SO lines.