transient--delete-window: Ensure buffer is always killed

The transient window is expected to be alive when this function is
called, so this shouldn't make a difference, but it also does not
hurt to be a bit defensive.

lisp/transient.el

@@ -2495,11 +2495,11 @@ value.  Otherwise return CHILDREN as is.")
           (if (window-parent win)
               (delete-window win)
             (delete-frame (window-frame win) t)))))
-      (when (buffer-live-p transient--buffer)
-        (kill-buffer transient--buffer))
-      (setq transient--buffer nil)
       (when remain-in-minibuffer-window
-        (select-window remain-in-minibuffer-window)))))
+        (select-window remain-in-minibuffer-window))))
+  (when (buffer-live-p transient--buffer)
+    (kill-buffer transient--buffer))
+  (setq transient--buffer nil))
 
 (defun transient--export ()
   (setq transient-current-prefix transient--prefix)