Improve xlsx performance

add changes to improve Xlsx parser

Bug: 577489

plugins/org.eclipse.gendoc.document.parser.xlsx/src/org/eclipse/gendoc/document/parser/xlsx/XLSXParser.java

diff --git a/plugins/org.eclipse.gendoc.document.parser.xlsx/src/org/eclipse/gendoc/document/parser/xlsx/XLSXParser.java b/plugins/org.eclipse.gendoc.document.parser.xlsx/src/org/eclipse/gendoc/document/parser/xlsx/XLSXParser.java
index 3d0d360..ba79f9e 100644
--- a/plugins/org.eclipse.gendoc.document.parser.xlsx/src/org/eclipse/gendoc/document/parser/xlsx/XLSXParser.java
+++ b/plugins/org.eclipse.gendoc.document.parser.xlsx/src/org/eclipse/gendoc/document/parser/xlsx/XLSXParser.java
@@ -51,6 +51,7 @@
 import org.eclipse.gendoc.document.parser.xlsx.helper.XPathXlsxUtils;
 import org.w3c.dom.Attr;
 import org.w3c.dom.Element;
+import org.w3c.dom.Node;
 import org.w3c.dom.NodeList;
 
 //TODO: Handel tr@r (§3.15.4); not supported due to be a woorkbook reference