Fix a edge case in the fetch related targets.

This would have given an error when:

• The port uses DIST_SUBDIR
• That sub-directory does not exist
• The current user does not have permission to write in DISTDIR.

Something like:

$ sudo rmdir /usr/ports/distfiles/gallery2
$ make fetch-urlall-list
mkdir: /usr/ports/distfiles/gallery2: Permission denied

• Error code 1

PR: 222819
Reported by: sunpoet
Sponsored by: Absolight