whisper: fix empty topic (#15811)

* whisper: fix empty topic

* whisper: add check to matchSingleTopic

* whisper: add tests

* whisper: fix gosimple

* whisper: added lastTopicByte const

1 files changed, 1 insertions, 1 deletions

diff --git a/whisper/whisperv6/api.go b/whisper/whisperv6/api.go
index 0e8490b41..2f6f671e9 100644
--- a/whisper/whisperv6/api.go
+++ b/whisper/whisperv6/api.go
@@ -567,7 +567,7 @@ func (api *PublicWhisperAPI) NewMessageFilter(req Criteria) (string, error) {
 	}
 
 	if len(req.Topics) > 0 {
-		topics = make([][]byte, 1)
+		topics = make([][]byte, 0, len(req.Topics))
 		for _, topic := range req.Topics {
 			topics = append(topics, topic[:])
 		}