consider when height is zero (cosmos#465)

relayer/tm-light-client.go

@@ -280,7 +280,7 @@ func (c *Chain) MustGetLatestLightHeight() uint64 {
  return uint64(height)
 }
 
-// GetLightSignedHeaderAtHeight returns a signed header at a particular height.
+// GetLightSignedHeaderAtHeight returns a signed header at a particular height (0 - the latest).
 func (c *Chain) GetLightSignedHeaderAtHeight(height int64) (*tmclient.Header, error) {
  // create database connection
  db, df, err := c.NewLightDB()
@@ -294,6 +294,13 @@ func (c *Chain) GetLightSignedHeaderAtHeight(height int64) (*tmclient.Header, er
  return nil, err
  }
 
+ if height == 0 {
+ height, err = client.LastTrustedHeight()
+ if err != nil {
+ return nil, err
+ }
+ }
+
  // VerifyLightBlock will return the header at provided height if it already exists in store,
  // otherwise it retrieves from primary and verifies against trusted store before returning.
  sh, err := client.VerifyLightBlockAtHeight(context.Background(), height, time.Now())