-/*
- Returns selected grn items:
-
- $grn_batch_id != 0 - only items for selected grn
- $supplier_id!='' - only items for selected supplier
- $outsanding_only==true - only not fully invoiced items
- $is_invoiced_only==true - only those which are at least partially invoiced
- $invoice_no!=0 - for selected invoice(s)
- $begin!='' or $end!='' - within selected delivery time range
-*/