Command execution via path-reduction validation bypass

Path traversal in Artifex Ghostscript before 10.03.1 allows local users to execute commands through a crafted PostScript document. In base/gpmisc.c, gp_validate_path_len reduces a path after recognizing its current-directory prefix, then skips two characters during fallback validation, turning a rejected parent path into an allowed path. Processing an attacker-supplied document is required; a filename such as aa/../%pipe%command# bypasses %pipe% controls and runs commands with the Ghostscript process's privileges.