Add Recursion Guards for Workdir

Ran the following in the same folder as build_root

fpm --workdir . --verbose -s dir -t deb -n clion -v 2026.1.1 -C build_root --description "A cross-platform IDE for C and C++ by JetBrains" --maintainer "RIGIK93" .

this turned into a recursive packaging as tmp was created inside the build_root, which immediately occupied all of the free space on my hard drive. Could you add a guard against such recursion for idiots like me?