remove check for ReaderFrom on underlying writer, as it may be badly implemented.

common/buf/writer.go

@@ -137,12 +137,8 @@ func (w *BufferedWriter) ReadFrom(reader io.Reader) (int64, error) {
 	}
 
 	w.buffered = false
-
-	if readerFrom, ok := w.writer.(io.ReaderFrom); ok {
-		return readerFrom.ReadFrom(reader)
-	}
-
 	err := Copy(NewReader(reader), w, CountSize(&sc))
+
 	return sc.Size, err
 }