Fix delete rows bug

Fixes #225

app/playlistmodel.py

@@ -363,12 +363,15 @@ class PlaylistModel(QAbstractTableModel):
 
         Need to delete them in contiguous groups wrapped in beginRemoveRows / endRemoveRows
         calls. To keep it simple, if inefficient, delete rows one by one.
+
+        TODO: delete in blocks
+
+        Delete from highest row back so that not yet deleted row numbers don't change.
         """
 
-        log.info(f"delete_rows({row_numbers=}")
-
         with Session() as session:
-            for row_number in row_numbers:
+            for row_number in sorted(row_numbers, reverse=True):
+                log.info(f"delete_rows(), {row_number=}")
                 super().beginRemoveRows(QModelIndex(), row_number, row_number)
                 # We need to remove data from the underlying data store,
                 # which is the database, but we cache in