XWPFDocument : line breaks converted to page breaks.

[PBrunot]

Description of the issue

Line breaks without type attribute in the XML file, are converted to Page Breaks by NPOI.

Reproduction of the issue

Opening a Word file, containing line breaks without a defined type attribute (e.g. <w:br />), as generated by Word when typing Shift+Enter , and saving it, is enought to see the issue.

            using var reader = File.OpenRead(cabTemplate.FullName);
            XWPFDocument doc = new XWPFDocument(new FileInputStream(reader));
            
            var dbg = Path.GetRandomFileName();
            using var outstr = File.Create(dbg);
            doc.Write(outstr);
            outstr.Close();

[tonyqus]

Thank you for the PR.