bug#18096: 24.3.92; async shell command and a busy buffer leads to error

[Nicolas Richard <theonewiththeevillook@yahoo.fr>]

Running the following and answering "yes" to the prompt leads to an error:

(let ((b (get-buffer-create "Some command")))
  (shell-command "sleep 1 &" b)
  (shell-command ":&" b))

Debugger entered--Lisp error: (wrong-type-argument stringp #<buffer Some command>)
  generate-new-buffer-name(#<buffer Some command>)
  generate-new-buffer(#<buffer Some command>)
  (setq buffer (generate-new-buffer (or output-buffer "*Async Shell Command*")))
  [hand-edited]
  shell-command(":&" #<buffer Some command>)

I suggest the following in order to have a better error message :

--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -2904,7 +2904,8 @@ the use of a shell (with its need to quote arguments)."
 		      (error "Shell command in progress")))
 		   ((eq async-shell-command-buffer 'confirm-new-buffer)
 		    ;; If will create a new buffer, query first.
-		    (if (yes-or-no-p "A command is running in the default buffer.  Use a new buffer? ")
+		    (if (and (stringp output-buffer)
+                             (yes-or-no-p "A command is running in the default buffer.  Use a new buffer? "))
 			(setq buffer (generate-new-buffer
 				      (or output-buffer "*Async Shell Command*")))
 		      (error "Shell command in progress")))

-- 
Nico.