Make desktop-kill more robust

* lisp/desktop.el (desktop-kill): Allow exiting Emacs even if we
can't delete the desktop file (bug#20762).

lisp/desktop.el

@@ -759,7 +759,10 @@ is nil, ask the user where to save the desktop."
        (unless (yes-or-no-p "Error while saving the desktop.  Ignore? ")
 	 (signal (car err) (cdr err))))))
   ;; If we own it, we don't anymore.
-  (when (eq (emacs-pid) (desktop-owner)) (desktop-release-lock))
+  (when (eq (emacs-pid) (desktop-owner))
+    ;; Allow exiting Emacs even if we can't delete the desktop file.
+    (ignore-error 'file-error
+      (desktop-release-lock)))
   t)
 
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