Allow session to re-try oval_results export
Allow session to re-try oval_results export

Recently, we are getting weird reports from ABRT retrace server such:
 1: oscap_htable_iterator_has_more
 2: ds_rds_create_from_dom (inlined) src/DS/rds.c +724
 3: ds_rds_create_source src/DS/rds.c +752
 4: xccdf_session_export_arf src/XCCDF/xccdf_session.c +1291
 5: app_evaluate_xccdf utils/oscap-xccdf.c +524

This commit may not fix it. However, I cannot reproduce original
segfault.

jan-cerny/openscap,openprivacy/openscap,OpenSCAP/openscap,Hexadorsimal/openscap,ybznek/openscap,ybznek/openscap,mpreisler/openscap,OpenSCAP/openscap,jan-cerny/openscap,jan-cerny/openscap,redhatrises/openscap,ybznek/openscap,jan-cerny/openscap,postfix/openscap,Hexadorsimal/openscap,redhatrises/openscap,Hexadorsimal/openscap,postfix/openscap,mpreisler/openscap,redhatrises/openscap,openprivacy/openscap,openprivacy/openscap,Hexadorsimal/openscap,OpenSCAP/openscap,jan-cerny/openscap,postfix/openscap,OpenSCAP/openscap,openprivacy/openscap,ybznek/openscap,mpreisler/openscap,mpreisler/openscap,postfix/openscap,ybznek/openscap,redhatrises/openscap,OpenSCAP/openscap,mpreisler/openscap,ybznek/openscap,jan-cerny/openscap,Hexadorsimal/openscap,redhatrises/openscap,openprivacy/openscap,mpreisler/openscap,openprivacy/openscap,OpenSCAP/openscap,postfix/openscap,redhatrises/openscap,postfix/openscap,Hexadorsimal/openscap