base: fix error printing deliveries with only \n in description

Default printout (used for order, packing lists, invoices etc) was raising
error for deliveries with cells when the resource descrption was only \n
7 jobs for fix/order-with-cell-description-backslash-n in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner1

01:29:39

passed ERP5.PerformanceTest-TestRunner1

00:31:08

passed ERP5.UnitTest-TestRunner1

01:26:33

failed ERP5.UnitTest-TestRunner1

02:29:27

canceled ERP5.UnitTest-TestRunner1

failed ERP5.UnitTest-TestRunner1

01:20:08

canceled ERP5.UnitTest-TestRunner1