fix(dirvish): guard nil file and reject path-traversal playlist names

cj/set-wallpaper passed `(dired-file-name-at-point)` straight to `expand-file-name`, so running it with no file at point raised a bare `wrong-type-argument` instead of a clear error. cj/dired-create-playlist-from-marked expanded the raw playlist name under `music-dir` without checking it, so a name like "../foo" or "/etc/foo" would write outside the music directory.

I added a nil-file guard to set-wallpaper and a `cj/--playlist-name-safe-p` check that rejects any name carrying a directory separator before the path is built. Both paths now fail cleanly with a user-error. Regression tests went into the existing wrapper and playlist test files.

1 files changed, 6 insertions, 0 deletions

diff --git a/tests/test-dirvish-config-wrappers.el b/tests/test-dirvish-config-wrappers.el
index 7072fcf7..bead4583 100644
--- a/tests/test-dirvish-config-wrappers.el
+++ b/tests/test-dirvish-config-wrappers.el
@@ -140,5 +140,11 @@ calls the wallpaper-setter binary."
     (should (member "/some/picture.jpg" call-process-args))
     (should (string-match-p "Wallpaper set" msg))))
 
+(ert-deftest test-dirvish-set-wallpaper-no-file-errors ()
+  "Error: with no file at point, set-wallpaper signals user-error rather
+than passing nil to expand-file-name."
+  (cl-letf (((symbol-function 'dired-file-name-at-point) (lambda () nil)))
+    (should-error (cj/set-wallpaper) :type 'user-error)))
+
 (provide 'test-dirvish-config-wrappers)
 ;;; test-dirvish-config-wrappers.el ends here