`org-file-contents': Improve error message

* lisp/org.el (org-file-contents): Improve error message.

lisp/org.el

@@ -5290,7 +5290,8 @@ is available.  This option applies only if FILE is a URL."
 	;; Move point to after the url-retrieve header.
 	(search-forward "\n\n" nil :move)
 	;; Search for the success code only in the url-retrieve header.
-	(if (save-excursion (re-search-backward "HTTP.*\\s-+200\\s-OK" nil :noerror))
+	(if (save-excursion
+	      (re-search-backward "HTTP.*\\s-+200\\s-OK" nil :noerror))
 	    ;; Update the cache `org--file-cache' and return contents.
 	    (puthash file
 		     (buffer-substring-no-properties (point) (point-max))
@@ -5306,7 +5307,8 @@ is available.  This option applies only if FILE is a URL."
 	      (buffer-string))
 	  (file-error
            (funcall (if noerror #'message #'user-error)
-		    (error-message-string err)))))))))
+		    "Unable to read file %S"
+		    file))))))))
 
 (defun org-extract-log-state-settings (x)
   "Extract the log state setting from a TODO keyword string.