Preserve user stats like play/skip counts when reloading song metadata when opening the edit tag dialog. Fixes issue 3359.

src/core/song.cpp

@@ -1180,3 +1180,12 @@ void Song::ToXesam(QVariantMap* map) const {
     AddMetadata("xesam:userRating", rating(), map);
   }
 }
+
+void Song::MergeUserSetData(const Song& other) {
+  set_playcount(other.playcount());
+  set_skipcount(other.skipcount());
+  set_lastplayed(other.lastplayed());
+  set_rating(other.rating());
+  set_score(other.score());
+  set_art_manual(other.art_manual());
+}

src/core/song.h

@@ -130,6 +130,11 @@ class Song {
   void ToWmdm(IWMDMMetaData* metadata) const;
 #endif
 
+  // Copies important statistics from the other song to this one, overwriting
+  // any data that already exists.  Useful when you want updated tags from disk
+  // but you want to keep user stats.
+  void MergeUserSetData(const Song& other);
+
   static QString Decode(const QString& tag, const QTextCodec* codec = NULL);
 
   // Save

src/library/librarywatcher.cpp

@@ -514,12 +514,7 @@ void LibraryWatcher::PreserveUserSetData(const QString& file, const QString& ima
   if (!out->has_embedded_cover())
     out->set_art_automatic(image);
 
-  out->set_playcount(matching_song.playcount());
-  out->set_skipcount(matching_song.skipcount());
-  out->set_lastplayed(matching_song.lastplayed());
-  out->set_rating(matching_song.rating());
-  out->set_score(matching_song.score());
-  out->set_art_manual(matching_song.art_manual());
+  out->MergeUserSetData(matching_song);
 
   // The song was deleted from the database (e.g. due to an unmounted 
   // filesystem), but has been restored.

src/ui/edittagdialog.cpp

@@ -216,8 +216,10 @@ QList<EditTagDialog::Data> EditTagDialog::LoadData(const SongList& songs) const
       Song copy(song);
       TagReaderClient::Instance()->ReadFileBlocking(copy.url().toLocalFile(), &copy);
 
-      if (copy.is_valid())
+      if (copy.is_valid()) {
+        copy.MergeUserSetData(song);
         ret << Data(copy);
+      }
     }
   }