fdo#72645: Allow GETPIVOTDATA to get result from leaf node of result tree.

Change-Id: I0fc1fd069440ed6fee378fc2dfd2ed761afbdeab
Reviewed-on: https://gerrit.libreoffice.org/7284
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>