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.

Refs #9950

Signed-off-by: Chris Pinkham <cpinkham@mythtv.org>
(cherry picked from commit db25a28)

mythtv/libs/libmythdb/mythdownloadmanager.cpp

@@ -651,6 +651,7 @@ 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_reply->abort();