Save first delay tag as timestamp

So far we got the first delay with a from that comes from the server.
This way we know it's MUC history.

Now we take the first time stamp we actually find. Which is likely the
one being added first. And should contain the correct time to display.

It would be nicer to actually compare the dates though.

Regards #1254

src/xmpp/message.c

@@ -838,6 +838,15 @@ _handle_groupchat(xmpp_stanza_t *const stanza)
         message->timestamp = stanza_get_delay_from(stanza, jid->domainpart);
     }
 
+    // Above we check whether the timestamps come from the server. So we know it
+    // is MUC history.
+    // Now we actually save the first timestamp we can find, since this is likely
+    // the first one being added. So the time should actually be right one to display.
+    // TODO: properly compare the dates
+    if (message->timestamp) {
+        message->timestamp = stanza_get_delay(stanza);
+    }
+
     if (message->timestamp) {
         sv_ev_room_history(message);
     } else {