io: remove manual SectionReader.Size in SectionReader.ReadAt
Change-Id: Ib3e8953dbdefa2b78c31b1bcbf0909bce248e423
Reviewed-on: https://go-review.googlesource.com/c/go/+/500475 Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Auto-Submit: Ian Lance Taylor <iant@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>