Add a timeout for RemoteFile sync. downloads in MythDownloadManager

In MythDownloadManager::downloadNow(), add a 20 second timeout for
RemoteFile downloads.  This allows us to abort a synchronous
RemoteFile download if the transfer hangs.  RemoteFile does not
send back progress updates, so we can't rely on m_lastStat being
updated, so we base the timeout on the start time.
(cherry picked from commit 156e8ba)

mythtv/libs/libmythdb/mythdownloadmanager.cpp

@@ -628,10 +628,16 @@ bool MythDownloadManager::downloadNow(MythDownloadInfo *dlInfo, bool deleteInfo)
     m_infoLock->unlock();
     m_queueWaitCond.wakeAll();
 
-    // sleep for 200ms at a time for up to 10 seconds waiting for the download
+    // timeout myth:// RemoteFile transfers 20 seconds from now
+    // timeout non-myth:// QNetworkAccessManager transfers 10 seconds after
+    //    their last progress update
+    QDateTime startedAt = QDateTime::currentDateTime();
     m_infoLock->lock();
     while ((!dlInfo->m_done) &&
-           (dlInfo->m_lastStat.secsTo(QDateTime::currentDateTime()) < 10))
+           (((!dlInfo->m_url.startsWith("myth://")) &&
+             (dlInfo->m_lastStat.secsTo(QDateTime::currentDateTime()) < 10)) ||
+            ((dlInfo->m_url.startsWith("myth://")) &&
+             (startedAt.secsTo(QDateTime::currentDateTime()) < 20))))
     {
         m_infoLock->unlock();
         m_queueWaitLock.lock();