core: prevent calling catalog with an empty list

Folder_getDeleteObjectList could do an extra paranaoïa check that the
caller did not pass an empty list of uids, because this would cause the
script to iterate on the full catalog table.
6 jobs for <span class="ref-name">feat/erp5_core_vs_pylint</span> in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner1

02:01:19

failed ERP5.PerformanceTest-TestRunner1

00:35:00

failed ERP5.UnitTest-TestRunner1

02:57:34

passed ERP5.CodingStyleTest-TestRunner1

01:03:47

failed ERP5.PerformanceTest-TestRunner1

00:33:41

failed ERP5.UnitTest-TestRunner1

02:50:27