The check for BLI_path_normalize having succeeded only checked for a trailing "../" which isn't correct. This caused going up a directory in the file selector to do nothing on directories ending with "..". This also caused an empty path to expand into "../" because BLI_path_extension_check didn't account for this case. Resolve using BLI_path_name_at_index which extracts the last component of the path without having to match the the surrounding slashes.