b2: Don't re-read the SHA1 if we already have it

b2/b2.go

@@ -614,12 +614,13 @@ func (o *Object) Hash(t fs.HashType) (string, error) {
 	if t != fs.HashSHA1 {
 		return "", fs.ErrHashUnsupported
 	}
-
+	if o.sha1 == "" {
 		// Error is logged in readFileMetadata
 		err := o.readFileMetadata()
 		if err != nil {
 			return "", err
 		}
+	}
 	return o.sha1, nil
 }