Fix typo

Indeed a weird one...

src/include/facts.sh

             *)   suffix=MKIT_BUG;
                  warn "MKIT_BUG: bad dirt/commit detection" ;;
         esac
-        test -b "$prerl" && suffix="-$prerl$suffix"
+        test -n "$prerl" && suffix="-$prerl$suffix"
         version="$version$suffix"
     fi
     echo "$version"