[PATCH STABLE] debugcolor: fix crash by empty styles (issue5856)

[Augie Fackler]

> On Apr 26, 2018, at 08:34, Yuya Nishihara <yuya at tcha.org> wrote:
> 
> # HG changeset patch
> # User Yuya Nishihara <yuya at tcha.org>
> # Date 1524745453 -32400
> #      Thu Apr 26 21:24:13 2018 +0900
> # Branch stable
> # Node ID 2098173ebe1bd9273e10028fa446eb23b4ca1322
> # Parent  7dffecb148aa77184b19c054e301345b3b51af1b
> debugcolor: fix crash by empty styles (issue5856)

queued, thanks