[UI] Fix useReceiveLineItems bug (#12756) (#12757)

- Prevent negative pre-fill values

(cherry picked from commit f8328cd1db)

Co-authored-by: Oliver <oliver.henry.walters@gmail.com>

src/frontend/src/forms/PurchaseOrderForms.tsx

@@ -907,7 +907,7 @@ export function useReceiveLineItems(props: LineItemsForm) {
             // here would make the backend treat this line as if the user
             // had explicitly chosen the PO's default, blocking any override.
             location: elem.destination ?? null,
-            quantity: elem.quantity - elem.received,
+            quantity: Math.max(0, elem.quantity - elem.received),
             expiry_date: null,
             batch_code: '',
             serial_numbers: '',