Throw exception if PdfReader instance is attempted to be reused between PdfDocument instances

ITXT-CR-938

Autoported commit.
Original commit hash: [5ef108935]

Author: yulian-gaponenko

itext.tests/itext.kernel.tests/itext/kernel/pdf/PdfReaderTest.cs

@@ -1447,6 +1447,19 @@ public virtual void WrongStructureFlushingTest() {
             pdfDoc.Close();
         }
 
+        /// <exception cref="System.IO.IOException"/>
+        [NUnit.Framework.Test]
+        public virtual void ReaderReuseTest() {
+            NUnit.Framework.Assert.That(() =>  {
+                String filename = sourceFolder + "hello.pdf";
+                PdfReader reader = new PdfReader(filename);
+                PdfDocument pdfDoc1 = new PdfDocument(reader);
+                PdfDocument pdfDoc2 = new PdfDocument(reader);
+            }
+            , NUnit.Framework.Throws.InstanceOf<PdfException>().With.Message.EqualTo(PdfException.PdfReaderHasBeenAlreadyUtilized))
+;
+        }
+
         private bool ObjectTypeEqualTo(PdfObject @object, PdfName type) {
             PdfName objectType = ((PdfDictionary)@object).GetAsName(PdfName.Type);
             return type.Equals(objectType);

itext/itext.kernel/itext/kernel/PdfException.cs

@@ -389,6 +389,8 @@ public class PdfException : Exception {
 
         public const String PdfPagesTreeCouldBeGeneratedOnlyOnce = "PdfPages tree could be generated only once.";
 
+        public const String PdfReaderHasBeenAlreadyUtilized = "Given PdfReader instance has already been utilized. The PdfReader cannot be reused, please create a new instance.";
+
         public const String PdfStartxrefIsNotFollowedByANumber = "PDF startxref is not followed by a number.";
 
         public const String PdfStartxrefNotFound = "PDF startxref not found.";

itext/itext.kernel/itext/kernel/pdf/PdfDocument.cs

@@ -1842,6 +1842,9 @@ protected internal virtual void Open(PdfVersion newPdfVersion) {
             try {
                 EventCounterHandler.GetInstance().OnEvent(CoreEvent.PROCESS, properties.metaInfo, GetType());
                 if (reader != null) {
+                    if (reader.pdfDocument != null) {
+                        throw new PdfException(PdfException.PdfReaderHasBeenAlreadyUtilized);
+                    }
                     reader.pdfDocument = this;
                     reader.ReadPdf();
                     foreach (ICounter counter in GetCounters()) {

port-hash

@@ -1 +1 @@
-0d18957af8d5ed66a1d178136cbec93ebbb2ac29
+5ef108935f7f77dc71b1fc1550df0c0e10a58696