PDFBOX-5283: ignore dublicate object keys when correcting xRefs

Author: Schmidor

pdfbox/src/main/java/org/apache/pdfbox/pdfparser/COSParser.java

@@ -1320,8 +1320,13 @@ private Map<COSObjectKey, Long> bfSearchForObjects() throws IOException
                             if (lastObjOffset > 0)
                             {
                                 // add the former object ID only if there was a subsequent object ID
-                                bfCOSObjectKeyOffsets.put(
-                                        new COSObjectKey(lastObjectId, lastGenID), lastObjOffset);
+                                COSObjectKey objectKey = new COSObjectKey(lastObjectId, lastGenID);
+                                if(!bfCOSObjectKeyOffsets.containsKey(objectKey)) {
+                                    bfCOSObjectKeyOffsets.put(objectKey, lastObjOffset);
+                                } else {
+                                    LOG.debug("Ignoring duplicate object key (" + objectKey
+                                            + ")");
+                                }
                             }
                             lastObjectId = objectId;
                             lastGenID = genID;