playlist: a better crash fix in pl_item_copy

include/deadbeef/deadbeef.h

@@ -1078,6 +1078,12 @@ typedef struct {
     DB_playItem_t * (*pl_item_alloc_init) (const char *fname, const char *decoder_id);
     void (*pl_item_ref) (DB_playItem_t *it);
     void (*pl_item_unref) (DB_playItem_t *it);
+
+    // Copy playlist item with metadata.
+    // NOTE: There's a behavior change from 1.9.6 to the next version:
+    // The older version was copying the previous/next pointers into the original linked lists (both main and search).
+    // This was required by some ancient version of deadbeef,
+    // but in the current one it causes a crash bug / data corruption under certain circumstances.
     void (*pl_item_copy) (DB_playItem_t *out, DB_playItem_t *in);
 
     // request lock for adding files to playlist

src/playlist.c

@@ -1876,10 +1876,6 @@ pl_item_copy (playItem_t *out, playItem_t *it) {
     out->endsample64 = it->endsample64;
     out->shufflerating = it->shufflerating;
     out->_duration = it->_duration;
-    out->next[PL_MAIN] = it->next[PL_MAIN];
-    out->prev[PL_MAIN] = it->prev[PL_MAIN];
-    out->next[PL_SEARCH] = it->next[PL_SEARCH];
-    out->prev[PL_SEARCH] = it->prev[PL_SEARCH];
 
     for (DB_metaInfo_t *meta = it->meta; meta; meta = meta->next) {
         pl_add_meta_copy (out, meta);
@@ -3886,10 +3882,6 @@ plt_copy_items (playlist_t *to, int iter, playlist_t *from, playItem_t *before,
         if (items[i]) {
             playItem_t *new_it = pl_item_alloc ();
             pl_item_copy (new_it, items[i]);
-            new_it->next[PL_MAIN] = NULL;
-            new_it->prev[PL_MAIN] = NULL;
-            new_it->next[PL_SEARCH] = NULL;
-            new_it->prev[PL_SEARCH] = NULL;
             pl_insert_item (after, new_it);
             pl_item_unref (new_it);
             after = new_it;