a bit optimization

weed/mount/filehandle_read.go

@@ -47,6 +47,8 @@ func (fh *FileHandle) readFromChunks(buff []byte, offset int64) (int64, int64, e
 	if fileSize == 0 {
 		glog.V(1).Infof("empty fh %v", fileFullPath)
 		return 0, 0, io.EOF
+	} else if offset == fileSize {
+		return 0, 0, io.EOF
 	} else if offset >= fileSize {
 		glog.V(1).Infof("invalid read, fileSize %d, offset %d for %s", fileSize, offset, fileFullPath)
 		return 0, 0, io.EOF