Bug 66425: Avoid a NullPointerException found via oss-fuzz

We try to avoid throwing NullPointerException, but it was possible
to trigger one here with a specially crafted input-file

Should fix https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=62074

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1912125 13f79535-47bb-0310-9956-ffa450edef68

poi-ooxml/src/main/java/org/apache/poi/xssf/eventusermodel/XSSFReader.java

@@ -380,6 +380,10 @@ public class XSSFReader {
          */
         @Override
         public InputStream next() {
+            if (!sheetIterator.hasNext()) {
+                throw new IllegalStateException("Cannot get next from iterator");
+            }
+
             xssfSheetRef = sheetIterator.next();
 
             String sheetId = xssfSheetRef.getId();

poi-ooxml/src/main/java/org/apache/poi/xssf/usermodel/XSSFWorkbook.java

@@ -831,7 +831,7 @@ public class XSSFWorkbook extends POIXMLDocument implements Workbook, Date1904Su
     private XSSFName createAndStoreName(CTDefinedName ctName) {
         XSSFName name = new XSSFName(ctName, this);
         namedRanges.add(name);
-        namedRangesByName.put(ctName.getName().toLowerCase(Locale.ENGLISH), name);
+        namedRangesByName.put(ctName.getName() == null ? null : ctName.getName().toLowerCase(Locale.ENGLISH), name);
         return name;
     }