S3: fail fast when "X-Amz-Copy-Source" is a folder

fix https://github.com/chrislusf/seaweedfs/issues/2593

weed/s3api/s3api_object_copy_handlers.go

@@ -38,6 +38,10 @@ func (s3a *S3ApiServer) CopyObjectHandler(w http.ResponseWriter, r *http.Request
 			s3err.WriteErrorResponse(w, r, s3err.ErrInvalidCopySource)
 			return
 		}
+		if entry.IsDirectory {
+			s3err.WriteErrorResponse(w, r, s3err.ErrInvalidCopySource)
+			return
+		}
 		entry.Extended = weed_server.SaveAmzMetaData(r, entry.Extended, isReplace(r))
 		err = s3a.touch(dir, name, entry)
 		if err != nil {