Fix displayed tracker messages

Before this change, we were displaying debug messages constructed by
libtorrent, now we show messages returned by trackers.

Closes #8739.

src/base/bittorrent/torrenthandle.cpp

@@ -1511,7 +1511,7 @@ void TorrentHandle::handleTrackerWarningAlert(const libtorrent::tracker_warning_
     const QString message = QString::fromStdString(p->msg);
 #else
     const QString trackerUrl = p->tracker_url();
-    const QString message = QString::fromStdString(p->message());
+    const QString message = p->warning_message();
 #endif
 
     // Connection was successful now but there is a warning message
@@ -1527,7 +1527,7 @@ void TorrentHandle::handleTrackerErrorAlert(const libtorrent::tracker_error_aler
     const QString message = QString::fromStdString(p->msg);
 #else
     const QString trackerUrl = p->tracker_url();
-    const QString message = QString::fromStdString(p->message());
+    const QString message = p->error_message();
 #endif
 
     m_trackerInfos[trackerUrl].lastMessage = message;