kiss: fix _pkg_find for extra colons in KISS_PATH

Previously, having an extra colon in KISS_PATH causes / to be a
directory being searched in, so you could get things like

    $ KISS_PATH=: kiss s usr
    /usr

which is clearly incorrect.

kiss

@@ -337,6 +337,7 @@ _pkg_find() {
     # Intentional.
     # shellcheck disable=2086
     for _find_path in $4 "${3:-$sys_db}"; do set +f
+        ok "$_find_path" || continue
         for _find_pkg in "$_find_path/"$1; do
             test "${3:--d}" "$_find_pkg" && set -f -- "$@" "$_find_pkg"
         done