a couple bugfixes

chain/store/index.go

@@ -58,7 +58,7 @@ func (ci *ChainIndex) GetTipsetByHeight(ctx context.Context, from *types.TipSet,
 		if lbe.ts.Height() == to || lbe.parentHeight < to {
 			return lbe.ts, nil
 		} else if to > lbe.ts.Height()-ci.skipLength {
-			return ci.walkBack(from, to)
+			return ci.walkBack(lbe.ts, to)
 		}
 
 		cur = lbe.target
@@ -71,6 +71,13 @@ func (ci *ChainIndex) fillCache(tsk types.TipSetKey) (*lbEntry, error) {
 		return nil, err
 	}
 
+	if ts.Height() == 0 {
+		return &lbEntry{
+			ts:           ts,
+			parentHeight: 0,
+		}, nil
+	}
+
 	// will either be equal to ts.Height, or at least > ts.Parent.Height()
 	rheight := ci.roundHeight(ts.Height())
 

chain/store/store.go

@@ -946,7 +946,7 @@ func (cs *ChainStore) GetTipsetByHeight(ctx context.Context, h abi.ChainEpoch, t
 	}
 
 	if h > ts.Height() {
-		return nil, xerrors.Errorf("looking for tipset with height less than start point")
+		return nil, xerrors.Errorf("looking for tipset with height greater than start point")
 	}
 
 	if h == ts.Height() {