fix: from_warehouse getting set to None

[noahjacob]

Issue

Manufacturing Settings

• "Allow Multiple Material Consumption" is enabled.

Work Order Settings

• "Skip Material Transfer to WIP Warehouse" is enabled while creating the work order.
• When this setting is enabled, the WIP Warehouse field is not mandatory and can be left empty.
• When the WIP is empty, while clicking on "Finish" to create the stock entry, the source warehouses would get set to None since it wasn't handled.

Fix

• If WIP Warehouse is empty, it would set the item's set source warehouse in the stock entry detail.