mythfilldatabase: reduce memory usage.

Mythfilldatabase uses QDomDocument to parse and store the XML data that is read; according to QDomDocument documentation this object is not meant to handle large XML files; QXmlStreamReader should be used in these situations.

This commit replaces QDomDocument by QXmlStreamreader.

A test showed that memory usage dropped from 5.6 GB to 698 MB.

Fixes #13517

Signed-off-by: Peter Bennett <pbennett@mythtv.org>
(cherry picked from commit a9aa006)

mythtv/programs/mythfilldatabase/filldata.cpp

@@ -92,7 +92,6 @@ bool FillData::GrabDataFromFile(int id, QString &filename)
     ChannelInfoList chanlist;
     QMap<QString, QList<ProgInfo> > proglist;
 
-    m_xmltvParser.lateInit();
     if (!m_xmltvParser.parseFile(filename, &chanlist, &proglist))
         return false;