fix multiline tests

src/irc/irc_client.cpp

@@ -1528,7 +1528,7 @@ void IrcClient::process_batch(const std::string& reference_tag)
         for (const IrcMessage& message: it->second.second)
           {
             auto it_tags = message.tags.find("draft/multiline-concat");
-            if (it_tags == message.tags.end())
+            if (!body.empty() && it_tags == message.tags.end())
                 body += "\n" + message.arguments[1];
             else
                 body += message.arguments[1];