Fix#804, opened in Dec. 2018, and closed as stale in Feb. 2019, and which I have re-opened to be closed properly by this PR. Better late than never, I suppose. A third party generated an ODS spreadsheet which PhpSpreadsheet could not read. By way of explanation, the xml in the file contained lots of whitespace between tags, which is wonderful for those humans among us who have to analyze it; but PhpSpreadsheet was not prepared for it. It is now.