bug#24997: 26.0.50; ibuffer-decompose-filter has side effects on error

[Eli Zaretskii <eliz@gnu.org>]

> From: Tino Calancha <tino.calancha@gmail.com>
> Date: Wed, 23 Nov 2016 16:34:32 +0900
> 
> 
> M-x ibuffer RET
> / m lisp-interaction-mode RET
> / > 10 RET
> ;; here `ibuffer-filtering-qualifiers' has value:
> ;; ((size-gt . 10) (used-mode . lisp-interaction-mode))
> / d
> ;; Signals error:
> ibuffer-decompose-filter: Filter type size-gt is not compound
> 
> Note that previous command has side effects on `ibuffer-filtering-qualifiers'
> even when there is an error; after this command the var has value:
> ((used-mode . lisp-interaction-mode))
> 
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> >From 4540c12df119e247b5eb0a33c216375a43421e62 Mon Sep 17 00:00:00 2001
> From: Tino Calancha <tino.calancha@gmail.com>
> Date: Wed, 23 Nov 2016 16:28:49 +0900
> Subject: [PATCH] ibuffer-decompose-filter: Avoid side effects on error

Please always accompany bug fixes with a test, if that is feasible.

Thanks.