Fix server crash when receiving zero arg commands.

fix #246

controller/server/reader.go

@@ -223,6 +223,7 @@ moreData:
 		if !complete {
 			break
 		}
+		if len(args) > 0 {
 			if kind != kindHTTP {
 				msg.Command = strings.ToLower(string(args[0]))
 				for i := 0; i < len(args); i++ {
@@ -244,6 +245,7 @@ moreData:
 				return nil, errInvalidHTTP
 			}
 			msgs = append(msgs, msg)
+		}
 		data = leftover
 	}
 	if len(data) > 0 {