Bug 66425: Avoid a ClassCastException found via oss-fuzz

We try to avoid throwing ClassCastException, 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=61276

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1911536 13f79535-47bb-0310-9956-ffa450edef68

poi/src/main/java/org/apache/poi/hssf/record/TextObjectRecord.java

                 throw new RecordFormatException("Read " + ptgs.length
                         + " tokens but expected exactly 1");
             }
+            if (!(ptgs[0] instanceof OperandPtg)) {
+                throw new IllegalArgumentException("Had unexpected type of ptg at index 0: " + ptgs[0].getClass());
+            }
             _linkRefPtg = (OperandPtg) ptgs[0];
             _unknownPostFormulaByte = in.remaining() > 0 ? in.readByte() : null;
         } else {

poi/src/test/java/org/apache/poi/hssf/dev/BaseTestIteratingXLS.java

         excludes.put("61300.xls", RecordFormatException.class);
         // BIFF 5
         excludes.put("64130.xls", OldExcelFormatException.class);
+        // fuzzed binaries
+        excludes.put("clusterfuzz-testcase-minimized-POIHSSFFuzzer-6322470200934400.xls", RuntimeException.class);
         return excludes;
     }