do not increment unique entry count when replacing an existing entry

git-svn-id: https://svn.code.sf.net/p/jackcess/code/jackcess/trunk@1400 f203690c-595d-4dc9-a70b-905162fa7fd2

src/main/java/com/healthmarketscience/jackcess/impl/IndexData.java

@@ -685,7 +685,9 @@ public class IndexData {
   {
     if(newEntry != null) {
       dataPage.addEntry(idx, newEntry);
-      if(!isDupeEntry) {
+      // if we are adding a duplicate entry, or replacing an existing entry,
+      // then the unique entry count doesn't change
+      if(!isDupeEntry && (oldEntry == null)) {
         ++_uniqueEntryCount;
       }
       ++_modCount;