Fix for reading Namespaces only usend in root node

Author: Gianluca Giovinazzo

src/PhpSpreadsheet/Reader/Xml.php

@@ -324,6 +324,8 @@ public function loadIntoExisting($pFilename, Spreadsheet $spreadsheet)
         $xml = $this->trySimpleXMLLoadString($pFilename);
 
         $namespaces = $xml->getNamespaces(true);
+	$namespacesDoc = $xml->getDocNamespaces(true);
+	$namespaces = array_merge($namespaces, $namespacesDoc);
 
         $docProps = $spreadsheet->getProperties();
         if (isset($xml->DocumentProperties[0])) {