add another edge-case to the code that reads xref tables

add test

resolves DEVSIX-1426

Author: joris.schellekens

kernel/src/main/java/com/itextpdf/kernel/pdf/PdfReader.java

@@ -808,7 +808,7 @@ protected PdfDictionary readXrefSection() throws IOException {
                 tokens.nextValidToken();
                 int gen = tokens.getIntValue();
                 tokens.nextValidToken();
-                if (pos == 0L && gen == 65535 && num == 1) {
+                if (pos == 0L && gen == 65535 && num == 1 && start != 0) {
                     // Very rarely can an XREF have an incorrect start number. (SUP-1557)
                     // e.g.
                     // xref

kernel/src/test/java/com/itextpdf/kernel/pdf/CorruptXRefTest.java

@@ -0,0 +1,53 @@
+package com.itextpdf.kernel.pdf;
+
+import com.itextpdf.kernel.utils.CompareTool;
+import com.itextpdf.test.annotations.type.IntegrationTest;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+import java.io.IOException;
+
+import static com.itextpdf.test.ITextTest.createDestinationFolder;
+
+/**
+ * This test checks correct handling of pdf documents with (slightly) corrupt XREF table
+ * xref
+ * 0 30
+ * 0000000000 65535 f
+ * 0000000000 65535 f
+ */
+@Category(IntegrationTest.class)
+public class CorruptXRefTest {
+
+    public static final String sourceFolder = "./src/test/resources/com/itextpdf/kernel/pdf/CorruptXRefTest/";
+    public static final String outputFolder = "./target/test/com/itextpdf/kernel/pdf/CorruptXRefTest/";
+
+    @BeforeClass
+    public static void beforeClass() {
+        createDestinationFolder(outputFolder);
+    }
+
+    @Test
+    public void readPdfWithCorruptXRef() throws IOException, InterruptedException {
+        String cmpFile = sourceFolder + "cmp_docOut.pdf";
+        String outputFile = outputFolder + "docOut.pdf";
+        String inputFile = sourceFolder + "docIn.pdf";
+        PdfWriter writer = new PdfWriter(outputFile);
+
+        PdfReader reader = new PdfReader(inputFile);
+
+        PdfDocument inputPdfDocument = new PdfDocument(reader);
+        PdfDocument outputPdfDocument = new PdfDocument(writer);
+
+        int lastPage = inputPdfDocument.getNumberOfPages();
+        inputPdfDocument.copyPagesTo(lastPage, lastPage, outputPdfDocument);
+
+        inputPdfDocument.close();
+        outputPdfDocument.close();
+
+        Assert.assertNull(new CompareTool().compareByContent(outputFolder + "docOut.pdf", cmpFile, outputFolder, "diff_"));
+
+    }
+}