fix: Add check for Content-Type when downloading tracker list.

Check if the URL from where we are downloading the trackers returns `Content-Type` as `text`.
Otherwise consider it might be a non-usable format for this functionality (html,xml,etc.ect.)

src/base/net/downloadhandlerimpl.cpp

@@ -143,6 +143,7 @@ void Net::DownloadHandlerImpl::processFinishedDownload()
 #else
     m_result.data = m_reply->readAll();
 #endif
+    m_result.contentType = m_reply->header(QNetworkRequest::ContentTypeHeader).toString();
 
     if (m_downloadRequest.saveToFile())
     {

src/base/net/downloadmanager.h

@@ -107,6 +107,7 @@ namespace Net
         QByteArray data;
         Path filePath;
         QString magnetURI;
+        QString contentType;
     };
 
     class DownloadHandler : public QObject

src/gui/trackersadditiondialog.cpp

@@ -109,6 +109,13 @@ void TrackersAdditionDialog::onTorrentListDownloadFinished(const Net::DownloadRe
     m_ui->downloadButton->setEnabled(true);
     setCursor(Qt::ArrowCursor);
 
+    if (!result.contentType.contains(u"text/plain"_s, Qt::CaseInsensitive))
+    {
+        QMessageBox::warning(this, tr("Download trackers list error")
+            , tr("The content type of the downloaded file is not plain text. Content-Type: \"%1\"").arg(result.contentType));
+        return;
+    }
+
     if (result.status != Net::DownloadStatus::Success)
     {
         QMessageBox::warning(this, tr("Download trackers list error")