Fix MergeWithSameNamedOCGTest test to do not accept possible false positive

DEVSIX-6093

Autoported commit.
Original commit hash: [0a6dd44b9]

itext.tests/itext.kernel.tests/itext/kernel/utils/PdfMergerTest.cs

@@ -458,6 +458,9 @@ namespace iText.Kernel.Utils {
             }
             NUnit.Framework.Assert.IsNull(new CompareTool().CompareByContent(mergedDocument, cmpDocument, destinationFolder
                 ));
+            // We have to compare visually also because compareByContent doesn't catch the differences in OCGs with the same names
+            NUnit.Framework.Assert.IsNull(new CompareTool().CompareVisually(mergedDocument, cmpDocument, destinationFolder
+                , "diff_"));
         }
 
         private void MergePdfs(IList<FileInfo> sources, String destination) {

itext.tests/itext.kernel.tests/resources/itext/kernel/utils/PdfMergerTest/cmp_MergeWithSameNamedOCG.pdf

@@ -1,4 +1,3 @@
-On Layer 1 page 1
 On Layer 2 page 1
 On Layer 1 page 2
 On Layer 2 page 2

itext.tests/itext.kernel.tests/resources/itext/kernel/utils/PdfMergerTest/sameNamdOCGSource.pdf

@@ -1,4 +1,3 @@
-On Layer 1 page 1
 On Layer 2 page 1
 On Layer 1 page 2
 On Layer 2 page 2

itext/itext.kernel/itext/kernel/pdf/OcgPropertiesCopier.cs

@@ -230,6 +230,8 @@ namespace iText.Kernel.Pdf {
             foreach (PdfIndirectReference fromOcgRef in fromOcgsToCopy) {
                 PdfDictionary toOcg = (PdfDictionary)fromOcgRef.GetRefersTo().CopyTo(toDocument, false);
                 String currentLayerName = toOcg.GetAsString(PdfName.Name).ToUnicodeString();
+                // Here we check on existed layer names only in destination document but not in source document.
+                // That is why there is no something like layerNames.add(currentLayerName); after this if statement
                 if (layerNames.Contains(currentLayerName)) {
                     hasConflictingNames = true;
                     int i = 0;

port-hash

@@ -1 +1 @@
-9561a1aecf626a4609068b87fe76b467bc41cf21
+0a6dd44b90f5bc37df559d1f1b2e620d807a07a6