ATR-27081 - fix chain merging for mu_mu_munoL1
Closes ATR-27081
Only one line of real change:
- nSteps.append(len(cConfig.steps))
+ nSteps.extend(cConfig.nSteps)This was an old line from back in the original merging code but the output was never used before now so it never got altered for > 2 leg chains.
It took all day to debug so I've left in some of the new/improved debug statements (and fixed one that has a bug in it).
This should have no effect on anything in the menu (a diff with the menu from the clean nightly shows identical menu json files). ctests all pass.