Fix crash when accessing trackers and using libtorrent v0.15.x

src/qtorrenthandle.cpp

@@ -302,7 +302,7 @@ size_type QTorrentHandle::filesize_at(unsigned int index) const {
   return h.get_torrent_info().file_at(index).size;
 }
 
-const std::vector<announce_entry>& QTorrentHandle::trackers() const {
+const std::vector<announce_entry> QTorrentHandle::trackers() const {
   Q_ASSERT(h.is_valid());
   return h.trackers();
 }

src/qtorrenthandle.h

@@ -97,7 +97,7 @@ class QTorrentHandle {
     bool is_queued() const;
     QString file_at(unsigned int index) const;
     size_type filesize_at(unsigned int index) const;
-    const std::vector<announce_entry>& trackers() const;
+    const std::vector<announce_entry> trackers() const;
     torrent_status::state_t state() const;
     QString creator() const;
     QString comment() const;

src/trackerlist.cpp

@@ -231,7 +231,7 @@ void TrackerList::loadTrackers() {
   // Load actual trackers information
   QHash<QString, TrackerInfos> trackers_data = properties->getBTSession()->getTrackersInfo(h.hash());
   QStringList old_trackers_urls = tracker_items.keys();
-  const std::vector<announce_entry> &trackers = h.trackers();
+  const std::vector<announce_entry> trackers = h.trackers();
   for(std::vector<announce_entry>::const_iterator it = trackers.begin(); it != trackers.end(); it++) {
     QString tracker_url = misc::toQString(it->url);
     QTreeWidgetItem *item = tracker_items.value(tracker_url, 0);