Bug 66425: Avoid exceptions found via poi-fuzz

Fix one expected exception-text which is different
on newer Java versions

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=63142

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1913385 13f79535-47bb-0310-9956-ffa450edef68

poi-ooxml/src/main/java/org/apache/poi/xdgf/usermodel/section/geometry/Ellipse.java

@@ -59,6 +59,11 @@ public class Ellipse implements GeometryRow {
         for (CellType cell : row.getCellArray()) {
             String cellName = cell.getN();
 
+            if (cellName == null) {
+                throw new POIXMLException("Invalid cell '" + cellName
+                        + "' in Ellipse row");
+            }
+
             switch (cellName) {
                 case "X":
                     x = XDGFCell.parseDoubleValue(cell);