bug#28402: 25.2; shr.el uses shr-tag-img despite set shr-external-rendering-functions

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: v.schneidermann@gmail.com,  28402@debbugs.gnu.org
> Date: Thu, 05 Oct 2017 13:18:37 +0200
> 
> The old call calls virtually always ends up with
> 
> (funcall function dom)
> 
> The new code calls shr-indirect-call which will will then 
> 
> (funcall function dom)
> 
> So one extra function call for each node.

What if we make shr-indirect-call a defsubst?  Would that take care of
this issue?