io: fix SectionReader Seek to seek backwards

Fixes #899.

R=golang-dev, rminnich, adg
CC=golang-dev
https://golang.org/cl/1749041

diff --git a/src/pkg/io/io.go b/src/pkg/io/io.go
index dcdc883b1ba32f19fbc868d47c0cc14aa4492aa2..a41a674cea90ac6d919815390605e3950e147ff3 100644 (file)
--- a/src/pkg/io/io.go
+++ b/src/pkg/io/io.go
@@ -336,7 +336,7 @@ func (s *SectionReader) Seek(offset int64, whence int) (ret int64, err os.Error)
        case 2:
                offset += s.limit
        }
-       if offset < s.off || offset > s.limit {
+       if offset < s.base || offset > s.limit {
                return 0, os.EINVAL
        }
        s.off = offset