goprotobuf: Fix bug in GetExtensions.
It is documented to return nil when an extension is missing;
we weren't doing that.
LGTM=nigeltao
R=nigeltao
CC=golang-codereviews
https://codereview.appspot.com/107230043
diff --git a/proto/extensions.go b/proto/extensions.go
index c40b392..e592053 100644
--- a/proto/extensions.go
+++ b/proto/extensions.go
@@ -300,6 +300,9 @@
extensions = make([]interface{}, len(es))
for i, e := range es {
extensions[i], err = GetExtension(epb, e)
+ if err == ErrMissingExtension {
+ err = nil
+ }
if err != nil {
return
}