syncbase: Quote non-utf8 in store keys in ErrNoExist.

Change-Id: I55c3e1b62601d7374f9a218b82b1ae54c2ff6099
diff --git a/services/syncbase/store/util.go b/services/syncbase/store/util.go
index 7ca945f..a321957 100644
--- a/services/syncbase/store/util.go
+++ b/services/syncbase/store/util.go
@@ -5,6 +5,8 @@
 package store
 
 import (
+	"strconv"
+
 	"v.io/v23/context"
 	"v.io/v23/verror"
 	"v.io/v23/vom"
@@ -86,7 +88,7 @@
 	bytes, err := st.Get([]byte(k), nil)
 	if err != nil {
 		if verror.ErrorID(err) == ErrUnknownKey.ID {
-			return verror.New(verror.ErrNoExist, ctx, k)
+			return verror.New(verror.ErrNoExist, ctx, strconv.Quote(k))
 		}
 		return verror.New(verror.ErrInternal, ctx, err)
 	}