Allow chains that do not have any steps

While trying to add chains to the menu that do not have any steps this was the only place in which the fix was needed. Tagging @fpastore @tamartin In the next step we can use it to build streamers and other technical chains that are essentially costless.

Trigger/TriggerCommon/TriggerMenuMT/python/HLTMenuConfig/Menu/MenuComponents.py

@@ -437,9 +437,11 @@ class Chain(object):
     def setSeedsToSequences(self):
         """ Set the L1 seeds to the menu sequences """
         
-        # check if the number of seeds is enought for all the seuqences:
-        max_seq= max(len(step.sequences) for step in self.steps)
-        tot_seed=len(self.vseeds)
+        # check if the number of seeds is enought for all the seuqences, no action of no steps are configured
+        if len(self.steps) == 0:
+            return
+        max_seq  = max(len(step.sequences) for step in self.steps)
+        tot_seed = len(self.vseeds)
         if max_seq==tot_seed:
             for step in self.steps:
                 if len(step.sequences) == 0: