runtime: handle empty environment variables on Plan 9

LGTM=bradfitz, rsc
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/137920044

diff --git a/src/pkg/runtime/env_plan9.go b/src/pkg/runtime/env_plan9.go
index b6dcb4c1eaa09ee4a1e85cbd5fc0472eb070f31e..76e9867e030a5fea9fbdae6a56ea0dc212dfe821 100644 (file)
--- a/src/pkg/runtime/env_plan9.go
+++ b/src/pkg/runtime/env_plan9.go
@@ -31,6 +31,10 @@ func gogetenv(key string) string {
                return ""
        }
        n := seek(fd, 0, 2) - 1
+       if n <= 0 {
+               close(fd)
+               return ""
+       }
 
        p := make([]byte, n)