service/files::delete: Fix incorrect error when wrong owner
service/files::delete: Fix incorrect error when wrong owner

Also improve the variable name for easier understanding.

Signed-off-by: Florian Pritz <753f544d2d01592750fb4bd29251b78abcfc8ecd@xinu.at>

Bluewind/filebin,jreinert/filebin,jreinert/filebin,Bluewind/filebin,Bluewind/filebin,Bluewind/filebin,jreinert/filebin,jreinert/filebin,Bluewind/filebin,jreinert/filebin,jreinert/filebin