Consistently open workbook in readonly mode

The itemreaders provided by this project are reading only. So it makes
sense to open them with only read-only priviliges. We already did this
for the streaming version of the itemreader. With this commit we also
enable this for the regular itemreader.

Closes: #128

Author: mdeinum

spring-batch-excel/src/main/java/org/springframework/batch/extensions/excel/poi/PoiItemReader.java

@@ -81,7 +81,7 @@ protected void doClose() throws Exception {
 	protected void openExcelFile(final Resource resource, String password) throws Exception {
 		if (resource.isFile()) {
 			File file = resource.getFile();
-			this.workbook = WorkbookFactory.create(file, password, false);
+			this.workbook = WorkbookFactory.create(file, password, true);
 		}
 		else {
 			this.inputStream = resource.getInputStream();