Test without scratchpad: Do not fail reading data for integrationtests

It seems the XLS now has missing cells which cause an NPE
while checking for scratchpad-handlers

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1912407 13f79535-47bb-0310-9956-ffa450edef68

poi-integration/src/test/java/org/apache/poi/stress/StressMap.java

@@ -119,7 +119,7 @@ public void readExMap(Sheet sh) {
             Row row = iter.next();
 
             if (SCRATCH_IGNORE && handlerIdx > -1) {
-                String handler = row.getCell(handlerIdx).getStringCellValue();
+                String handler = row.getCell(handlerIdx) == null ? "" : row.getCell(handlerIdx).getStringCellValue();
                 if (SCRATCH_HANDLER.matcher(handler).find()) {
                     // ignore exception of ignored files
                     continue;