Milo: master grpc endpoint fix

milo/appengine/buildbot/grpc.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package buildbot
 
 import (
         "bytes"
         "compress/gzip"
         "encoding/json"
@@ skipping 75 matching lines @@
                 }
                 builder.CachedBuilds = make([]int, len(builds))
                 for i, b := range builds {
                         builder.CachedBuilds[i] = b.Number
                 }
         }
 
         // And re-compress it.
         gzbs := bytes.Buffer{}
         gsw := gzip.NewWriter(&gzbs)
-        defer gsw.Close()
         cw := iotools.CountingWriter{Writer: gsw}
         e := json.NewEncoder(&cw)
         if err := e.Encode(master); err != nil {
+                gsw.Close()
                 return nil, err
         }
+        gsw.Close()
 
         logging.Infof(c, "Returning %d bytes", cw.Count)
 
         return &milo.CompressedMasterJSON{
                 Internal: entry.Internal,
                 Modified: &google.Timestamp{
                         Seconds: entry.Modified.Unix(),
                         Nanos:   int32(entry.Modified.Nanosecond()),
                 },
                 Data: gzbs.Bytes(),
         }, nil
 }