master 3ba47a0782: Improve error when wallpaper-command is nil

[Stefan Kangas]

branch: master
commit 3ba47a0782f7059062ca6743b22c40a410933f13
Author: Stefan Kangas <stefankangas@gmail.com>
Commit: Stefan Kangas <stefankangas@gmail.com>

    Improve error when wallpaper-command is nil
    
    * lisp/image/wallpaper.el (wallpaper-set): Improve the error message
    when 'wallpaper-command' is nil.
---
 lisp/image/wallpaper.el | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lisp/image/wallpaper.el b/lisp/image/wallpaper.el
index d024d6238c..fe6882a588 100644
--- a/lisp/image/wallpaper.el
+++ b/lisp/image/wallpaper.el
@@ -254,6 +254,8 @@ On Haiku, no external command is needed, so the value of
         ((featurep 'haiku)
          (haiku-set-wallpaper file))
         (t
+         (unless wallpaper-command
+           (error "Couldn't find a command to set the wallpaper with"))
          (let* ((fmt-spec `((?f . ,(expand-file-name file))
                             (?h . ,(wallpaper--get-height-or-width
                                     "height"