Re #11398 Modified properties for LetMultirep system test

as this system test runs on a workspace, written without multirep_tof_range detectors properties, these properties have changed and can not be restored from the workspace.

Code/Mantid/Testing/SystemTests/tests/analysis/ISIS_LETReduction.py

@@ -190,6 +190,8 @@ def def_advanced_properties(self):
         # Should be possibility to define spectra_to_monitors_list to just monitors list, if
         # spectra_to_monitors_list remains undefined
         prop['spectra_to_monitors_list']=5506
+        # similar to the one above. old IDF do not contain this property
+        prop['multirep_tof_specta_list']="12416,21761"
         return prop
       #
     @iliad
@@ -226,7 +228,7 @@ def custom_name(prop_man):
             """
             # Note -- properties have the same names  as the list of advanced and
             # main properties
-            ei = prop_man.incident_energy
+            ei = PropertyManager.incident_energy.get_current()
             # sample run is more then just list of runs, so we use
             # the formalization below to access its methods
             run_num = PropertyManager.sample_run.run_number()