Quit the serialization when there is an object referencing itself in SmartModePdfObjectsSerializer

Test for the corresponding case was added to functional-tests repo: KERNEL_SmartMode_XObjectSelfReference#xObjectIterativeReference with input file name "checkboxes_XObject_iterative_reference.pdf".

DEVSIX-2137

Autoported commit.
Original commit hash: [680a4df24]

Author: Federico Frascarelli

itext/itext.kernel/itext/kernel/pdf/SmartModePdfObjectsSerializer.cs

@@ -87,12 +87,21 @@ public virtual SerializedObjectContent SerializeObject(PdfObject obj) {
             if (content == null) {
                 ByteBuffer bb = new ByteBuffer();
                 int level = 100;
-                SerObject(obj, bb, level, serializedCache);
+                try {
+                    SerObject(obj, bb, level, serializedCache);
+                }
+                catch (SmartModePdfObjectsSerializer.SelfReferenceException) {
+                    return null;
+                }
                 content = bb.ToByteArray();
             }
             return new SerializedObjectContent(content);
         }
 
+        private class SelfReferenceException : Exception {
+        }
+
+        /// <exception cref="iText.Kernel.Pdf.SmartModePdfObjectsSerializer.SelfReferenceException"/>
         private void SerObject(PdfObject obj, ByteBuffer bb, int level, IDictionary<PdfIndirectReference, byte[]> 
             serializedCache) {
             if (level <= 0) {
@@ -112,6 +121,11 @@ private void SerObject(PdfObject obj, ByteBuffer bb, int level, IDictionary<PdfI
                     return;
                 }
                 else {
+                    if (serializedCache.Keys.Contains(reference)) {
+                        //referencing itself
+                        throw new SmartModePdfObjectsSerializer.SelfReferenceException();
+                    }
+                    serializedCache.Put(reference, null);
                     savedBb = bb;
                     bb = new ByteBuffer();
                     obj = reference.GetRefersTo();
@@ -155,6 +169,7 @@ private void SerObject(PdfObject obj, ByteBuffer bb, int level, IDictionary<PdfI
             }
         }
 
+        /// <exception cref="iText.Kernel.Pdf.SmartModePdfObjectsSerializer.SelfReferenceException"/>
         private void SerDic(PdfDictionary dic, ByteBuffer bb, int level, IDictionary<PdfIndirectReference, byte[]>
              serializedCache) {
             bb.Append("$D");
@@ -171,6 +186,7 @@ private void SerDic(PdfDictionary dic, ByteBuffer bb, int level, IDictionary<Pdf
             bb.Append("$\\D");
         }
 
+        /// <exception cref="iText.Kernel.Pdf.SmartModePdfObjectsSerializer.SelfReferenceException"/>
         private void SerArray(PdfArray array, ByteBuffer bb, int level, IDictionary<PdfIndirectReference, byte[]> 
             serializedCache) {
             bb.Append("$A");

port-hash

@@ -1 +1 @@
-3f9bf568b8609a5307de7de96bbb5c1765a84394
+680a4df24ec910b99f69f92ed2867a2bd25a494a