Return appropriate error code from browse_stat_path() instead of trying to deal with the error internally.

Summary:
Current behavior of browse_stat_path() can result in both finished() and error() being signaled to KIO.
This patch adjusts the logic to prevent this case.

Reviewers: elvisangelaccio

BUG: 376344
FIXED-IN: 17.08.0

Differential Revision: https://phabricator.kde.org/D6617