Translate from leg ID to chain ID when checking active HLT jet chains

Multi-threshold jet chains were returning 0 counts because the previous decision object returned active "legs", which did not correspond to the tool chain IDs. We don't have separate tools for each leg in the jet signature, so the hypo tools were never activated.

By converting from the leg ID to the chain ID, the hypo alg registers that the tool is meant to be active.

FYI @tamartin, @peter, @jbossios