Fix a potential segfault if MDM::downloadNow() times out.

Reset the destination QByteArray pointer after a download
timeout to make sure the downloadFinished() callback doesn't
try to write to it after it has been deallocated.

Closes #9950

I'm leaving part 2 of #9950 uncommitted for now since we do
not need or use this functionality internally.

Signed-off-by: Chris Pinkham <cpinkham@mythtv.org>

mythtv/libs/libmythbase/mythdownloadmanager.cpp

@@ -665,6 +665,7 @@ bool MythDownloadManager::downloadNow(MythDownloadInfo *dlInfo, bool deleteInfo)
 
     if (!dlInfo->m_done)
     {
+        dlInfo->m_data = NULL;      // Prevent downloadFinished() from updating
         dlInfo->m_syncMode = false; // Let downloadFinished() cleanup for us
         if ((dlInfo->m_reply) &&
             (dlInfo->m_errorCode == QNetworkReply::NoError))