Mac QDirModel: subdirectories does not show up if the path is very long and has many subdirectories

On Mac with the QDirModel not all subdirectories show up if the path is very long and has many subdirectories.

Reproducible with /examples/itemviews/dirview :

1. Create the subfolder structure of more than 25 subfolders with the
path length about 2300 symbols;
2. Try to look at the deepest folder, you can't see it. The example
shows only 17 high subfolders in the structure.