wsman-filter: fix possible NULL dereferencing
wsman-filter: fix possible NULL dereferencing

Check for NULL from:
ws_xml_add_child
u_zalloc
u_malloc

Check right variable for NULL.

Signed-off-by: Alexander Usyskin <2c2d03d7dae842f113743879f565d486184f22a3@intel.com>

vcrhonek/openwsman,vcrhonek/openwsman,kkaempf/openwsman,vcrhonek/openwsman,vcrhonek/openwsman,Openwsman/openwsman,Openwsman/openwsman,Openwsman/openwsman,Openwsman/openwsman,Openwsman/openwsman,kkaempf/openwsman,kkaempf/openwsman,kkaempf/openwsman,vcrhonek/openwsman,Openwsman/openwsman,kkaempf/openwsman,vcrhonek/openwsman,vcrhonek/openwsman,kkaempf/openwsman,kkaempf/openwsman,Openwsman/openwsman