Clarify NeverFail logic.

Phys/Tesla/python/Tesla/Configuration.py

@@ -757,6 +757,10 @@ class Tesla(LHCbConfigurableUser):
                     DataCopy('Copy{0}'.format(loc.replace('/', '')),
                              What=loc,
                              Target=os.path.join(base, loc),
+                             # It's very possible that the extra locations
+                             # might not exist, so no relations table will be
+                             # created; we don't mind the copying failing in
+                             # those cases
                              NeverFail=True if loc.replace('Relations/', '/Event/') in (extra_track_locs + extra_proto_locs) else False,
                              OutputLevel=output_level)
                     for loc in relationsLocations