Short circuit genesis condition for new state mgmt (#5223)

* Fixed a regression. Genesis case for state gen

* Comment

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>

beacon-chain/state/stategen/getter.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/pkg/errors"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/shared/params"
 	"go.opencensus.io/trace"
 )
 
@@ -15,6 +16,11 @@ func (s *State) StateByRoot(ctx context.Context, blockRoot [32]byte) (*state.Bea
 	ctx, span := trace.StartSpan(ctx, "stateGen.StateByRoot")
 	defer span.End()
 
+	// Genesis case. If block root is zero hash, short circuit to use genesis state stored in DB.
+	if blockRoot == params.BeaconConfig().ZeroHash {
+		return s.beaconDB.State(ctx, blockRoot)
+	}
+
 	slot, err := s.blockRootSlot(ctx, blockRoot)
 	if err != nil {
 		return nil, errors.Wrap(err, "could not get state summary")