storage: avoid map reuse

Change-Id: I7f8c384dc9dd47b2706392188685a106a1ed487a
Reviewed-on: https://go-review.googlesource.com/36251
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/storage/client.go b/storage/client.go
index 5bb3b81..03749f0 100644
--- a/storage/client.go
+++ b/storage/client.go
@@ -180,6 +180,10 @@
 	if ul.err != nil {
 		return false
 	}
+
+	// Clear UploadInfo before decoding new value.
+	ul.ui = UploadInfo{}
+
 	ul.err = ul.dec.Decode(&ul.ui)
 	return ul.err == nil
 }