Do not detect clone entry as duplicated content.

If two entries point to the same tuple (cluter_id, blob_id), we must
not report them as duplicated content.

src/zimcheck/checks.cpp

@@ -350,7 +350,7 @@ class ArticleChecker
 
     // All article with the same hash will be recorded in the same bucket of
     // this hash table.
-    std::map<unsigned int, std::list<zim::entry_index_type>> hash_main;
+    std::map<unsigned int, std::list<std::tuple<zim::entry_index_type, zim::cluster_index_type, zim::blob_index_type>>> hash_main;
 
     zim::ConcurrentCache<std::string, bool> linkStatusCache;
 };
@@ -387,7 +387,7 @@ void ArticleChecker::check_item(const zim::Item& item)
         data = item.getData();
 
     if(checks.isEnabled(TestType::REDUNDANT))
-        hash_main[adler32(data)].push_back( item.getIndex() );
+        hash_main[adler32(data)].push_back( {item.getIndex(), item.getClusterIndex(), item.getBlobIndex()} );
 
     if (item.getMimetype() != "text/html")
         return;
@@ -487,14 +487,19 @@ void ArticleChecker::detect_redundant_articles()
         progress.report();
         auto l = it.second;
         while ( !l.empty() ) {
-            const auto e1 = archive.getEntryByPath(l.front());
+            const auto [e1_idx, e1_cluster_idx, e1_blob_idx] = l.front();
             l.pop_front();
+            const auto e1 = archive.getEntryByPath(e1_idx);
             if ( !l.empty() ) {
                 // The way we have constructed `l`, e1 MUST BE an item
                 const std::string s1 = e1.getItem().getData();
                 decltype(l) articlesDifferentFromE1;
                 for(auto other : l) {
-                    auto e2 = archive.getEntryByPath(other);
+                    const auto [e2_idx, e2_cluster_idx, e2_blob_idx] = other;
+                    if (e1_cluster_idx == e2_cluster_idx && e1_blob_idx == e2_blob_idx) {
+                        continue;
+                    }
+                    auto e2 = archive.getEntryByPath(e2_idx);
                     std::string s2 = e2.getItem().getData();
                     if (s1 != s2 ) {
                         articlesDifferentFromE1.push_back(other);